Dissertation SHohl_2015_online_final

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Dissertation SHohl_2015_online_final
MULTI'PROXY!ANALYSIS!OF!EDIACARAN!SHALLOW'!AND!DEEP!
WATER!CARBONATES,!YANGTZE!PLATFORM,!SOUTH!CHINA!
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S IMON! V. ! H OHL !
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Dissertation!submitted!in!partial!fulfilment!of!the!requirements!for!the!degree!of!!
Doktor&der&Naturwissenschaften&(Dr.&rer.&nat.)!
Fachbereich!Geowissenschaften!
Freie!Universität!Berlin!
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Supervisor:!Prof.!Dr.!Harry!Becker!
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September,!2015!'!Berlin,!Germany!
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Firstreferee(Erstgutachter):
Prof.Dr.HarryBecker,FachbereichGeowissenschaften,FreieUniversitätBerlin,Germany
Secondreferee(Zweitgutachter):
Prof.Dr.Shao-YongJiang,StateKeyLaboratoryofGeologicalProcessesandMineralResources,
FacultyofEarthResources,ChinaUniversityofGeosciences,Wuhan,PeoplesRepublicofChina
Dayofdefence(TagderDisputation):
03.11.2015
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ERKLÄRUNG!!
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Hiermit! erkläre! ich,! dass! die! vorliegende! Arbeit! selbstständig! und! ausschließlich! unter! der!
Verwendung! der! angegebenen! Hilfsmittel! und! Quellen! von! mir! verfasst! wurde.! Wörtlich! oder!
inhaltlich!übernommene!Stellen!habe!ich!als!solche!gekennzeichnet.!Ich!habe!diese!Arbeit!in!keinem!
früheren!Promotionsvorhaben!eingereicht.!
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Berlin,!den!02.09.2015!
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Summary'
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SUMMARY!
The! Ediacaran! era! (635! to! 542! Ma)! has! seen! some! of! the! largest! geochemical! fluctuations!
and! biological! innovations! in! Earth! history.! The! change! from! icehouse! to! greenhouse! climate!
resulted! in! melting! of! low! latitude! Marinoan! ice! sheets! and! presumably! triggered! the! radiation! of!
early!animals!at!the!Precambrian/Cambrian!boundary.!Contemporaneous!oxygenation!of!the!Earth’s!
atmosphere! and! presumably! the! deeper! oceanic! realms! further! led! to! evolution! of! metazoans,!
predation!and,!as!a!result,!extended!bio'mineralisation.!!
The! Doushantuo! Formation! on! the! Yangtze! Platform,! South! China,! is! an! ideal! archive! of!
temporal!and!spatial!geochemical!changes!in!the!late!Neoproterozoic!oceans,!as!it!spans!90!%!of!the!
Ediacaran! (635! ±! 0.6! to! 551! ±! 0.7! Ma)! and! was! deposited! under! shallow'! to! deep! water! marine!
environmental!conditions.!
The! major! scope! of! this! thesis! is! to! understand! the! geochemical! variations! in! Ediacaran!
marine!carbonates!and!link!them!to!environmental!changes.!Therefore!carbonate!rock!leachates!of!
the! Doushantuo! (and! overlying! Dengying)! lithologies! from! the! shallow! water! Xiaofenghe! (Hubei!
Province)! and! deep! water! Yanwutan! section! (Hunan! Province)! have! been! sampled.! These! samples!
were! investigated! for! their! major'! and! trace! element! concentrations! as! well! as! for! their! 87Sr/86Sr,!
δ18Ocarb!and!δ13Ccarb!isotopic!compositions.!Radiogenic!Sr!and!stable!C!and!O!isotopes!were!used!to!
distinguish!between!pristine!marine!precipitates!and!those!whose!isotopic!compositions!have!been!
modified! by! post! depositional! fluid! flow.! Paleo'seawater! conditions,! such! as! oxygenation! of! the!
water!body!and!seawater'freshwater!mixing!were!inferred!from!shale!normalised!REE+Y!patterns!of!
pristine! carbonates.! Redox'sensitive! elements! were! used! to! assess! pore'water! redox! conditions! in!
the!sediments.!Furthermore,!the!Nd!isotopic!composition!of!shallow!water!carbonates!was!analysed!
to!deduce!the!provenance!of!the!lanthanide!source!of!the!Yangtze!Platform!sediments.!
Finally!this!thesis!aims!to!test!whether!Cd!isotopes!may!be!used!to!pinpoint!the!onset!of!bio'
diversification! and! the! appearance! of! early! animals! before! the! Cambrian! explosion.! Therefore! Cd!
isotopes! were! analysed! together! with! δ13Corg,! δ15N,! TOC! and! N! concentrations! in! carbonates! and!
mudstones!from!the!extreme!shallow!water!section!Xiaofenghe,!Hubei!Province.!
This!thesis!provides!deeper!insight!into!carbonate!diagenesis!and!focuses!on!the!recognition!
of!pristine,!open!marine!seawater!geochemical!signatures!from!signatures!modified!by!either!mixing!
with!freshwater!or!diagenetic!overprint.!Deep!water!carbonates!at!Yanwutan!section!show!a!distinct!
overprint!by!continental!basin!fluids,!strongly!modifying!the!isotope!composition!of!the!sediments.!
Despite!this,!marine!REE+Y!patterns!are!commonly!still!preserved!in!these!lithologies.!Shallow!water!
carbonates! at! Xiaofenghe! section! reveal! minor! diagenetic! overprint.! However,! the! influence! of!
terrestrial! lanthanide! input,! presumably! brought! in! by! freshwater! influx! via! estuarine! mixing!
processes,!strongly!modified!REE+Y!patterns!in!the!very!shallow!to!lagoonal!Xiaofenghe!section.!!
N!and!Cd!isotopic!compositions!of!mudstones!and!carbonates!in!the!same!stratigraphic!units!
reveal! distinct! fluctuations! that! cannot! be! explained! by! biological! fractionation! alone.! Hence,! δ15N!
variations! might! be! the! result! of! isotope! fractionation! during! diagenetic! N'loss.! The! variation! in!
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! 1!
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Summary'
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ε112/110Cd! may! be! caused! by! isotope! fractionation! during! Cd! incorporation! in! sulphides! and! likely!
modified!by!salinity'dependent!fractionation!during!carbonate!precipitation.!The!work!suggests!that!
the!Cd!isotope!composition!of!Neoproterozoic!carbonates,!unlike!modern!marine!precipitates,!may!
not!be!used!as!proxy!for!biological!Cd!utilisation.!It!is!likely!that!the!modern!enzyme!responsible!for!
the! isotopically! selective! Cd! utilisation! in! phytoplankton! may! not! have! been! active! in! Precambrian!
organisms!yet.!
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Summary'
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ZUSAMMENFASSUNG!
Das!Ediakarium!(635!bis!542!Ma)!war!eine!Periode!gewaltiger!geochemischer!Umwälzungen!
und!biologischer!Innovationen.!Der!Wechsel!von!der!marinoischen!Eiszeit!zum!Treibhausklima!ging!
einher!mit!massivem!Abschmelzen!der!Eispanzer!und!mag!durch!den!damit!verbunden!Eintrag!von!
Nährstoffen!von!den!Kontinenten!mit!als!Auslöser!für!die!folgende!Evolution!von!Metazoen!gedient!
haben.!Des!Weiteren!trug!die!zeitgleiche!Sauerstoffanreicherung!der!Atmosphäre!und!der!tieferen!
Schichten! der! Ozeane! zur! Evolution! der! Mehrzeller,! sowie! der! Entwicklung! von! Jagdverhalten! und!
daraus!resultierend!zur!Entwicklung!von!Biomineralisation!als!Abwehrmechanismus!bei.!
Die!Doushantuo!Formation!auf!der!Yangtse!Plattform!in!Südchina!gilt!als!perfekte!Lokalität!
zur!Erfoschung!von!zeitlichen!wie!auch!räumlichen!geochemischen!Veränderungen!im!ediakarischen!
Ozean.! Die! Formation! wurde! auf! 635! ±! 0.6! bis! 551! ±! 0.7! Millionen! Jahre! vor! heute! datiert! und!
umfasst! damit! etwa! 90! %! des! gesamten! Ediakariums,! des! Weiteren! finden! sich! in! ihr!
unterschiedliche!Ablagerungsräume!vom!Flach'!bis!hin!zum!Tiefwaser!vereint.!!
Das! Hauptanliegen! dieser! Arbeit! besteht! darin,! die! geochemischen! Variationen! in!
ediakarischen! Karbonaten! besser! zu! verstehen! und! durch! diese! auf! die! sich! verändernden!
Umweltbedingungen! im! Ediakarium! zurück! zu! schließen.! Dafür! wurden! Karbonatauszüge! von!
Doushantuo!(und!darüber!anstehnden!Dengying)!Lithologien!des!Flachwasserprofils!bei!Xiaofenghe!
(Hubei! Provinz)! und! des! Tiefwasserprofils! bei! Yanwutan! (Hunan! Provinz)! untersucht.! Von! den!
Proben! wurden! Haupt'! und! Spurenelementkonzentrationen! sowie! 87Sr/86Sr,! δ18Ocarb! und! δ13Ccarb!
Isotopenzusammensetzungen! bestimmt.! Radiogene! Sr'! und! stabile! O'! und! C'isotopenverhältnisse!
wurden! als! Indikator! zur! Abgrenzung! von! diagenetisch! überprägten! zu! pristinen! Karbonatproben!
genutzt.! Paleo'Meerwasserbedingungen,! wie! die! Sauerstoffsättigung! oder! der! Einfluss! von!
Frischwasser,! wurden! mittels! PAAS! normalisierter! Seltener! Erden! Muster! bestimmt.! Die! Analyse!
redox'sensitiver!Elemente!diente!schließlich!dazu!Porenwasser!Redoxbedingungen!zu!erfassen.!Nd'
Isotopenverhältnisse! in! den! Flachwasserkarbonaten! wurden! zur! Bestimmung! der! Herkunft! der!
Lanthanidenquelle!in!den!Karbonaten!analysiert.!
Abschließend! wurde! mit! der! Arbeit! versucht! Cd! Isotope! als! Indikator! für! das! Einsetzen!
verstärkter! Biodiversität! und! dem! Aufkommen! der! ersten! Tierstämme! im! späten! Ediakarium! zu!
etablieren.! Daher! wurden! neben! Cd! in! Karbonaten! auch! N! Isotopenverhältnisse! in! organikreichen!
Lithologien! zusammen! mit! TOC! und! N! Konzentrationen! sowie! δ13Corg! Werten! im! Xiaofenghe!
Flachwasserprofil!bestimmt.!!
Die! Arbeit! gibt! weitergehende! Einblicke! in! die! Karbonatdiagenese! und! versucht! die!
Unterschiede! zwischen! pristinen! und! offenmarinen! geochemischen! Signaturen! von! überprägten!
Signaturen! in! Karbonatgesteinen! (letztere! durch! Diagenese! oder! Mischung! von! Wassermassen)! zu!
charakterisieren.! Daraus! resultierend,! haben! die! Tiefwasserproben! des! Yanwutan! Profils! eine!
stärkere!diagenetische!Überprägung!der!Isotopensignaturen!als!die!Flachwasserkarbonate!erfahren.!
Diese! Überprägung! läst! sich! vermutlich! auf! die! Reaktion! der! Karbonate! mit! kontinentalen!
Beckenfluiden! zurückführen.! Diese! Überprägung! hat! jedoch! im! allgmeinen! die! marinen! seltenen!
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Summary'
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Erden! Muster! der! Karbonate! nicht! verändert.! Dahingegen! zeigen! die! Flachwasserkarbonate! von!
Xiaofenghe!eine!Veränderung!der!seltenen!Erden!Muster!durch!verstärkten!Eintrag!der!Lanthaniden!
in!Flussmündungsnähe.!
N! und! Cd! Isotopenzusammensetzungen! in! organikreichen! Tonsteinen! und! Karbonaten! der!
gleichen!stratigraphischen!Einheit!zeigen!starke!Veränderungen!durch!das!Ediakarium.!Diese!lassen!
sich!nicht!allein!auf!biologische!Isotopenfraktionierung!zurückführen.!δ15N!Variationen!könnten!auch!
auf!Isotopenfraktionierung!bei!diagenetischer!Stickstoffabfuhr!im!Sediment!zurückzuführen!sein.!Die!
Variationen!in!ε112/110Cd!werden!möglicherweise!durch!Isotopenfraktionierung!bei!einem!selektiven!
Einbau!von!Cd!in!Sulphide!unter!euxinischen!Bedingungen,!sowie!salinitätsabhängiger!Fraktionierung!
in! Karbonate! gesteuert.! Als! Resultat! der! Arbeit! wird! daher! angenommen,! dass! die! Cd!
Isotopenzusammensetzung! von! neoproterozoischen! Karbonaten! nicht! von! biologischer!
Fraktionierung! gesteuert! wurde.! Anders! als! bei! modernen! marinen! Sedimenten! war! damit! das!
Enzym,!das!für!die!Cd!Isotopenfraktionierung!beim!Einbau!des!Cd!in!phytoplanktonische!Organismen!
verantwortlich!ist,!im!Präkambrium!vermutlich!noch!nicht!aktiv.!
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4!
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!
Summary'
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635
542Ma
Marinoan
/
!
δ
90
635!±!0.6
!551!±!0.7Ma
!
δ
ε
87
13
Sr! /! 86Sr
18
Ocarb
Ccarb
/
Nd
!
13
ε
Corg
15
TOC
N
!
'
REE! +! Y
ε
REE!+!Y
!
'
N
112/! 110
15
N
Cd
!
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! 5!
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ACKNOWLEDGEMENT!OF!FINANCIAL!SUPPORT!
!
The!German!Research!Foundation,!DFG:!
DFG!Research!Group!FOR!736!“The!Precambrian'Cambrian!Biosphere!Revolution:!Insights!from!
Chinese!Microcontinents”,!subproject!Be!1820/4'2!to!H.!Becker!!
!
The!National!Science!Foundation!of!China,!NSFC:!
Grants!(41230102,!41273009)!and!a!973!project!(2013CB835000)!to!SY!Jiang!and!JH!Yang!
!
Center!for!International!Cooperation!at!Freie!Universität!Berlin:!
Travel!grant!to!Nanjing!University!for!laboratory!work,!spring!2013!(to!H.!Becker)!
!
Confucius!Scholarship,!China!
Intensive!language!course!grant!at!Nanjing!University,!spring!2015!(to!S.V.!Hohl)!
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6!
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ACKNOWLEDGEMENTS!
!
I!would!like!to!thank!Monika!Feth!and!Konrad!Hammerschmidt!for!their!support!in!the!lab!
and!the!Members!of!FOR!736!who!helped!in!sampling!the!analysed!rocks!in!the!field!in!South!China!
and!other!members!for!their!helpful!discussions,!especially!Christoph!Heubeck!and!Xiaojuan!Sun!for!
providing! sedimentology! feedback! and! Michael! Tatzel! for! invaluable! input! during! daylong!
discussions.!!
I!would!like!to!thank!Uwe!Wiechert!for!his!help!analysing!O!and!C!isotopic!compositions!in!
carbonates,!Frank!Ohnemüller!and!the!University!of!Bremen,!Central!Laboratory!for!Crystallography!
and! Applied! Material! Sciences! for! XRD! analysis! and! Antonia! Gamper! and! the! staff! of! Museum! für!
Naturkunde!for!their!contributions!to!stable!isotope!data.!!
Thanks!also!to!the!Chinese!contributors!of!the!Sino'German!Research!Group,!in!particular!to!
Shao'Yong!Jiang!from!the!China!University!of!Geosciences!in!Wuhan!for!his!help!in!revising!my!work
From! Nanjing! University! I! would! like! to! thank! Jing'Hong! Yang! and! Hai'Zhen! Wei! for! their! help!
analysing!Nd!isotopic!compositions!and!Hong'Fei!Ling,!Da!Li,!and!all!members!of!their!group!for!their!
heartily!welcome!in!Nanjing.!!
Further!I!thank!Steve!Galer!and!Wafa!Abouchami!and!the!scientific!staff!at!the!Max!Planck!
Institute!für!Chemie!in!Mainz!for!their!help!analysing!Cd!isotopes.!!
Finally!I!would!like!to!thank!my!wonderful!friends!in!Bonn,!Berlin,!Seoul,!New!York,!Shanghai!
and!Nanjing!as!well!as!my!parents!for!their!long!lasting!support.!
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TABLE!OF!CONTENTS&
CHAPTER!1!!
INTRODUCTION!
1.1&The&Ediacaran&period!
1.2&OCEAN&OXIDATION&DURING&THE&TERMINAL&PROTEROZOIC!
1.3&RESEARCH&GOALS&AND&SCOPE&OF&THE&THESIS!
1.4&MAIN&CHAPTERS&OF&THE&THESIS!
1.4.1!CHAPTER!2!(PUBLISHED!IN!GEOCHIMICA!ET!COSMOCHIMICA!ACTA!2015.!163,!262'278)'
1.4.2!CHAPTER!3!(MANUSCRIPT!SUBMITTED!TO!PRECAMBRIAN!RESEARCH)'
1.4.3!CHAPTER!4!(UNPUBLISHED!MANUSCRIPT)'
1.5&REFERENCES!
11'
11'
13'
14'
17'
17'
17'
18'
19'
CHAPTER!2!!
MULTIPROXY&CONSTRAINTS&ON&ALTERATION&AND&PRIMARY&COMPOSITIONS&OF&EDIACARAN&&
DEEP&WATER&CARBONATE&ROCKS,&YANGTZE&PLATFORM,&SOUTH&CHINA!
2.1&ABSTRACT!
2.2&INTRODUCTION!
2.3&GEOLOGICAL&SETTING!
2.4&MATERIAL&AND&METHODS!
2.5&Results!
2.5.1!SR!ISOTOPIC!COMPOSITIONS:'
2.5.2!MAJOR'!AND!TRACE!ELEMENT!CONCENTRATIONS'
2.6&Discussion!
2.6.1!POST'DEPOSITIONAL!DIAGENESIS!OF!CARBONATES'
2.6.2!ORIGIN!OF!ABUNDANCE!VARIATIONS!IN!REE+Y'
2.6.3!ORIGIN!OF!ABUNDANCE!VARIATIONS!OF!REDOX'SENSITIVE!ELEMENTS'
2.6.4!MODELL!FOR!THE!TRACE!ELEMENTAL!BUDGET!IN!YANWUTAN!CARBONATES!AND!EFFECTS!OF!REDUCING!PORE'
WATERS'
2.7&CONCLUSION!
2.8&ACKNOWLEDGMENTS!
2.9&REFERENCES!
2.10&APPENDICES!
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22!
22'
23'
25'
28'
29'
29'
30'
33'
33'
37'
41'
46'
48'
49'
50'
55'
CHAPTER!3!
SECULAR&CHANGES&OF&WATER&CHEMISTRY&IN&SHALLOW&WATER&EDIACARAN&OCEAN:&EVIDENCE&
FROM&CARBONATES&AT&XIAOFENGHE,&THREE&GORGES&AREA,&YANGTZE&PLATFORM,&S.&CHINA! 59'
3.1&ABSTRACT!
59'
3.2&INTRODUCTION!
60'
3.3&GEOLOGIC&BACKGROUND!
63'
3.4&SAMPLES&AND&ANALYTICAL&METHODS!
66'
8!
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3.4.1!XRD'
3.4.2!STABLE!ISOTOPE!SYSTEMATICS'
3.4.3!ORGANIC!CARBON!ISOTOPE!COMPOSITIONS!AND!TOC!CONCENTRATIONS'
3.4.4!TRACE!ELEMENTS!AND!SR!ISOTOPIC!COMPOSITIONS'
3.4.5!ND!ISOTOPIC!COMPOSITIONS'
3.5&RESULTS!
3.5.1!MINERALOGY'
3.5.2!CARBON!AND!OXYGEN!ISOTOPIC!COMPOSITIONS'
3.5.3!ND!AND!SR!ISOTOPIC!COMPOSITIONS'
3.5.4!MAJOR'!AND!REDOX'SENSITIVE!ELEMENT!COMPOSITIONS'
3.5.5!RARE!EARTH!ELEMENTS'
3.6.&DISCUSSION!
3.6.1!THE!ROLE!OF!DIAGENETIC!FLUID'FLOW!OVERPRINT'
3.6.2!CONTROLS!ON!RARE!EARTH!ELEMENTS'YTTRIUM!VARIATIONS'
3.6.3!THE!ROLE!OF!FRESHWATER'SEAWATER!MIXING'
3.6.4!SR!AND!ND!ISOTOPIC!COMPOSITIONS!AND!THEIR!RELEVANCE!IN!LOCAL!SEAWATER'FRESHWATER!MIXING'
3.6.5!ORIGIN!OF!CLAY!MINERALS!IN!CARBONATE!ROCKS!AT!XIAOFENGHE'
3.7&CONCLUSIONS!
3.8&ACKNOWLEDGEMENTS!
3.9&REFERENCES!
APPENDICES:!
66'
66'
67'
67'
68'
69'
69'
71'
71'
72'
73'
76'
76'
78'
82'
87'
90'
91'
92'
93'
99'
CHAPTER!4!
CADMIUM&ISOTOPE&VARIATIONS&IN&NEOPROTEROZOIC&CARBONATES&[&A&TRACER&FOR&REDOX&
PROCESSES&AND&WATER&MASS&MIXING?!
4.1&ABSTRACT!
4.2&INTRODUCTION!
4.3&GEOLOGIC&BACKGROUND,&SAMPLE&SELECTION&AND&METHODS!
4.4&RESULTS!
4.5&DISCUSSION!
4.5.1!INFLUENCE!OF!TERRESTRIAL!INPUT'
4.5.2!DIAGENESIS'
4.5.3!POSSIBLE!CD!FRACTIONATION!EFFECTS!TO!BE!TESTED:'
4.5.3.1!BIOLOGICAL!FRACTIONATION'
4.5.3.2!REDOX!CONTROLLED!FRACTIONATION'
4.5.3.3!SALINITY!CONTROLLED!FRACTIONATION'
4.6&CONCLUSIONS!
4.7&ACKNOWLEDGEMENTS!
4.8&REFERENCES!
120'
120'
121'
122'
124'
126'
126'
126'
127'
127'
128'
130'
132'
133'
134&
CHAPTER!5!
140'
CONCLUSIONS!
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! 9!
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CHAPTER!6!
SCIENTIFIC&OUTPUT!
6.1&PEER&REVIEWED&PUBLICATIONS!
6.2&SUBMITTED&MANUSCRIPTS!
6.3&UNPUBLISHED&MANUSCRIPTS!
6.4&CONFERENCE&ABSTRACTS&AND&PRESENTATIONS!
6.5&GRADUATE&THESIS&SUPERVISION!
142'
142'
142'
142'
143'
143'
APPENDIX!
A &I:&F IELD&WORK&
A&II:&ANALYTICAL&PROTOCOL&
A &III:&C URRICULUM&VITAE!
!
144'
144!
146!
150'
10!
!
!!
!
Chapter'1:'Introduction'
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CHAPTER&1&
!
INTRODUCTION!
1.1!The!Ediacaran!period!
The!Ediacaran!era!represents!the!terminal!period!of!the!Neoproterozoic.!It!is!!characterised!
by! fundamental! global! environmental! changes,! including! the! increasing! oxygenation! of! the!
atmosphere! and! oceans! (Knoll! et! al.,! 2004)! as! well! as! biological! innovations! such! as! the! first!
appearance! of! acanthomorphic! acritarchs! (Zhou! and! Xiao,! 2007),! the! evolution! of! multicellular! life!
(e.g.! Xiao! et! al.,! 1998;! Yin! et! al.,! 2007;! 2011),! the! Ediacaran! biota! (e.g.! Waggoner,! (2003)! and!
references!therein),!and!the!first!bio'mineralising!animal!Cloudina!(Grant,!1989).!
The!Ediacaran!!starts!with!the!deposition!of!a!globally!occurring!characteristic!cap!carbonate!
stratum! that! overlies! glacial! deposits! of! the! low'latitude! Marinoan! glaciation! (Kirschvink,! 1992).! A!
GSSP!point!at!the!base!of!the!Nuccaleena!Formation!cap!carbonates!(Flinders!Range,!South!Australia)!
defines!the!beginning!of!the!era!(Knoll!et!al.,!2006)!and!U'Pb!zircon!ages!from!ash!beds!within!cap!
carbonates! from! the! base! of! the! Doushantuo! Formation! (Yangtze! Gorges,! South! China)! date! their!
deposition!635.2!±!0.6!Ma!ago!(Condon!et!al.,!2005).!!
The! melting! of! the! presumably! global! Marinoan! glaciation! was! most! likely! a! result! of!
elevated!pCO2!in!the!atmosphere,!triggering!super'greenhouse!conditions!(Hoffman,!1998).!Coeval!
silicate!weathering!(Kennedy!et!al.,!2006)!along!biological!induced!weathering!by!the!emergence!of!
fungi!and!lichen!biota!on!land!(e.g.!Kump,!2014)!may!have!increased!the!total!nutrient!flux!into!the!
oceans! during! the! Ediacaran! period.! This! flux! presumably! led! to! increased! P/Fe! ratios! recorded! in!
post!Marinoan!iron!formations!(Planavsky!et!al.,!2010),!may!account!for!the!rising! 87Sr/86Sr!record!in!
marine!carbonates!during!the!Neoproterozoic!and!could!have!finally!triggered!the!rise!of!animal!life!
at!the!end!of!the!Neoproterozoic!(e.g.!Kennedy,!2006).!
!
!
&&&&&&
!11!
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!
Chapter'1:'Introduction'
!
!
Ediacaran! marine! sediments! host! major! perturbations! in! the! carbon! cycle! of! the! ocean.!
Following! the! globally! occurring! negative! δ13Ccarb! excursions! in! Marinoan! cap! carbonates,! negative!
δ13Ccarb!values!occurring!in!some!carbonate!successions!around!the!globe!(e.g.!Newfoundland)!580!
Ma! ago! are! believed! to! indicate! the! localised! Gaskiers! glaciation! (Krogh! et! al.,! 1988).! The! middle!
Ediacaran! further! hosts! the! most! pronounced! negative! δ13C! inorganic! carbon! anomaly! in! Earth’s!
history!with!values!in!successions!of!Oman!dropping!down!to!a!nadir!of!'12!‰"(Le"Guerroue"́et"al.,"
2006).!This!so!called!Shuram'Wonoka!anomaly!has!been!identified!in!carbonate!sections!around!the!
globe,!yet!its!origin!is!highly!debated.!Hypotheses!include!oxidation!of!a!huge!dissolved!carbon!pool!
in!the!deep!ocean!during!the!rise!of!atmospheric!and!ocean!pO2!levels!(Fike!et!al.,!2006,!McFadden!
et!al.,!2008),!methane!oxidation!(Bjerrum!and!Canfield,!2011)!and!a!burial!diagenesis!origin!(Derry,!
2010a;! Swart! and! Kennedy! 2011).! Together! with! reasonable! doubts! that! the! Shuram'Wonoka!
anomaly!reflects!primary!seawater!compositions!more!and!more!publications!challenge!the!role!of!
carbon! isotopes! as! reliable! proxies! for! inter'platform! or! even! global! correlation! of! Ediacaran!
successions!(e.g.!Derry!2010b).!
While!early!work!on!the!Ediacaran!mostly!focused!on!the!evolution!and!global!correlation!of!
the!carbon!isotopic!composition!in!the!Ediacaran!ocean!(Kaufman!et!al.,!1997;!M.!Zhu!et!al.,!2007),!
nowadays!the!tool!box!has!been!enlarged!to!include!a!range!of!geochemical!proxies!that!have!been!
applied! to! Ediacaran! sediments! around! the! world.! To! gather! insights! into! paleo'weathering! rates!
researchers!are!using!Sr!and!Ca!isotope!compositions!(Kasemann!et!al.,!2005;!Pokrovsky!et!al.,!2011;!
Sawaki! et! al.,! 2008)! and! paleo'seawater! pH! may! be! inferred! from! boron! isotope! compositions!
(Ohnemueller!et!al.,!2014).!Other!isotope!systems!such!as!Si,!N,!and!Zn!isotopes!are!used!to!study!
the!effect!of!the!biological!fractionation!of!these!stable!isotope!systems!during!the!onset!of!complex!
multicellular!life!(Ader!et!al.,!2014;!Cremonese!et!al.,!2013;!Fan!et!al.,!2014;!Kunzmann!et!al.,!2012).!
Sulphur,! Fe,! Mo! and! Cr! isotopic! compositions! as! well! as! iron! speciation! and! redox'sensitive! trace!
element!analysis!(Canfield!et!al.,!2008;!Fan!et!al.,!2014;!Frei!et!al.,!2011;!Wen!et!al.,!2011)!are!used!
to!gather!information!about!ocean!and!atmosphere!redox!conditions!and!to!test!recent!models!of!a!
redox! stratified! Ediacaran! ocean! developed! on! the! Yangtze! Platform! (e.g.! Li! et! al.,! 2010).!
Furthermore,!numerous!studies!have!shown!that!ratios!and!patterns!of!the!rare!earth!elements!(REE)!
and!yttrium!in!carbonate!rocks!not!only!mirror!the!patterns!of!these!elements!in!water!from!which!
they! precipitated! (Kamber! and! Webb,! 2001;! Nothdurft! et! al.,! 2004;! Webb! and! Kamber,! 2000)! but!
also!yield!information!about!the!paleo'seawater!oxidation!state!(e.g.!Ling!et!al.,!2013).!
!
12!
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!
Chapter'1:'Introduction'
!
!
1.2!OCEAN!OXIDATION!DURING!THE!TERMINAL!PROTEROZOIC!
The!evolution!of!the!modern!oxygen'rich!atmosphere!and!oceans!apparently!occurred!in!two!major!
steps.! The! first! major! oxygenation! step! to! levels! higher! than! 10'5! present! atmospheric! level! (PAL)!
was! discovered! by! the! diminishing! of! mass'independent! fractionation! (MIF)! signals! of! sulphur!
isotopes! in! sediments! younger! than! 2.45! Ga! (e.g.! Farquhar! 2000).! The! second! major! oxygenation!
step! took! place! in! the! late! Neoproterozoic! 0.8! '! 0.6! Ma! ago.! It! was! until! then,! that! deep! ocean!
ventilation! was! not! completely! achieved! and! bio'essential! but! redox'sensitive! metals! bound! in!
anoxic! deep! ocean! sediments! were! not! as! available! as! in! modern! oceans.! This! restraint! of! bio'
essential! metals! may! also! have! restricted! the! evolution! of! animals! before! the! late! Neoproterozoic!
(e.g.!Anbar!and!Knoll,!2002).!!
Some! striking! geochemical! results! from! global! occurring! terminal! Proterozoic! marine!
sediment!records!suggest!that!the!oceans!of!this!period!finally!underwent!a!stepwise!and!protracted!
oxidation!(e.g.!Li!et!al.,!2010).!For!example!the!fractionation!of!sulphur!isotopes!shifted!from!mass'
independent! fractionation! before! the! GOE! to! mass! dependent! fractionation.! The! S! isotope!
compositions! of! the! Neoproterozoic! were! presumably! influenced! by! the! development! of! non'
photosynthetic!sulphide'oxidising!organisms,!leading!to!increasing!Δ34S!values!due!to!oxygenation!of!
the! atmosphere! and! the! persistent! ventilation! of! the! deep! ocean! (e.g.! Canfield! and! Teske,! 1996;!
Canfield,! 1998).! Further! arguments! for! the! oxygenation! of! the! oceans! and! atmosphere! in! the!
terminal! Proterozoic! are:! long'living! prolonged! positive! δ13Ccarb! values! with! some! (but! extreme)!
negative!δ13Ccarb!excursions!like!the!Shuram'Wonoka!(which!represents!the!largest!relative!change!in!
δ13Ccarb!in!geologic!time!(e.g.!Kaufman!and!Knoll,!1995)),!authigenic!accumulations!of!Mo!and!other!
redox'sensitive!metals!in!sulfidic!black!shales!towards!the!end!of!the!Neoproterozoic!(e.g.!Scott!et!al.,!
2008),!increasing!negative!Ce!anomalies!in!carbonates!at!the!Ediacaran/Cambrian!boundary!(Ling!et!
al.,!2013)!and!positive!δ53Cr!excursions!in!Ediacaran!carbonates!(Frei!et!al.,!2009).!
The!reasons!for!the!oxygenation!in!the!late!Neoproterozoic!are!still!debated.!Canfield!et!al.!
(2007)! and! Planavsky! et! al.! (2010)! suggested! that! glacial! melting! increased! nutrient! influx! and!
postglacial! phosphate! flux! to! the! oceans,! triggering! primary! productivity! and! subsequent! burial! of!
organic! matter! (OM).! The! publications! by! Derry! (2006)! and! Kump! (2014)! point! out! that! the!
weathering! environment! on! the! land! surface! changed! from! a! solely! physical! to! a! biochemical!
weathering!due!to!the!evolution!of!fungi!and!lichen!leading!to!the!formation!of!fine!grained!soils!and!
burial!of!OM!after!riverine!transportation!into!the!ocean.!OM!burial!finally!resulted!in!a!net!increase!
!
&&&&&&
!13!
!!
!
Chapter'1:'Introduction'
!
!
in!pO2!as!less!oxygen!is!consumed!for!its!oxidation.!An!alternative!hypothesis!by!Lenton!et!al.!(2014)!
is!the!establishment!of!a!positive!feedback!system!of!evolution!of!complex!eukaryotes,!benthic!filter!
feeding,!phosphorous!removal!and!deep!ocean!oxygenation.!
However,!while!more!and!more!geochemical!studies!point!out!that!deep!ocean!basins!could!
have!been!completely!oxygenated!by!the!end!of!the!Neoproterozoic!(Fike!et!al.,!2006;!Scott!et!al.,!
2008),! Canfield! et! al.! (2008)! suggested! a! conflict! with! evidence! for! anoxic! deep! waters! with!
ferruginous! (Fe2+! enriched)! or! even! euxinic! (sulphides! present)! conditions! persisting! into! the!
Cambrian.! The! redox! stratified! ocean! model! by! Li! et! al.! (2010)! showed! that! a! deep! anoxic! ocean!
might! have! maintained! on! the! Yangtze! Platform! throughout! the! whole! Ediacaran! period.! A! recent!
publication! by! Sperling! et! al.! (2015)! even! argues,! on! the! base! of! a! statistical! evaluation! of! iron!
speciation! data! through! Earth’s! history! that! the! terminal! Proterozoic! oxygenation! was! limited! and!
significant!rise!in!ocean'atmosphere!oxygen!to!present!levels!did!not!happen!before!the!Palaeozoic!
era.!!
!
!
!
1.3!RESEARCH!GOALS!AND!SCOPE!OF!THE!THESIS!
This! dissertation! is! part! of! the! larger! framework! of! the! Sino'German! DFG! Research! Group!
FOR!736!“The.Precambrian4Cambrian.Biosphere.Revolution:.Insights.from.Chinese.Microcontinents”.!
The!research!project!focused!on!marine!sediments!on!the!Yangtze!Platform!(South!China)!from!the!
late! early! Ediacaran! (above! the! glaciogenic! sediments! of! the! Marinoan! glaciation)! to! the! early!
Cambrian.! The! objective! of! the! project! was! to! understand! the! underlying! processes! of! the!
Precambrian/Cambrian! bio'radiation! by! constraining! paleo'environmental! conditions! using! a!
multidisciplinary!(sedimentology,!palaeontology,!and!geochemistry)!approach.!!
The!occurrence!of!shallow'!and!deep!water!sedimentary!facies!has!established!the!Yangtze!
Platform!in!South!China!as!a!key!area!for!the!study!of!Neoproterozoic!ocean!oxidation!and!Ediacaran!
animal!evolution!following!the!Marinoan!glaciation.!The!Doushantuo!Formation!directly!overlies!the!
tillites! of! the! Marinoan! Nantuo! Formation.! It! has! been! precisely! dated! between! 635.2! ±! 0.6! and!
551.1!±!0.7!Ma!and!spans!about!90!%!of!the!Ediacaran!(Condon!et!al.,!2005)!and!due!to!its!in!most!
sections! continuous! marine! sediment! record! it! is! ideal! for! high'resolution! geochemical! analysis! of!
paleo'ocean! chemistry.! Furthermore! the! Doushantuo! and! overlying! Dengying! strata! contain! a! vast!
fossil!record,!including!animal!embryos!and!macroscopic!algae!(Xiao!et!al.,!1998).!!
14!
!!
!
Chapter'1:'Introduction'
!
!
The! aim! of! this! thesis! is! to! understand! the! geochemical! variations! in! Ediacaran! marine!
carbonates! from! the! Yangtze! platform! and! link! them! to! environmental! changes.! Therefore!
carbonate! rock! leachates! of! the! Doushantuo! and! overlying! Dengying! lithologies! from! the! shallow!
water!Xiaofenghe!(Hubei!Province)!and!deep!water!Yanwutan!section!(Hunan!Province)!have!been!
sampled.! Together! with! my! supervisor! Harry! Becker! and! several! collaborators! from! Germany! and!
China!we!investigated!marine!sediments!for!their!major'!and!trace!element!concentrations!as!well!
as!for!their!Sr,!Nd,!C,!O,!N!and!Cd!isotopic!compositions.!Radiogenic!Sr!and!stable!C!and!O!isotopes!
were! used! to! distinguish! between! pristine! marine! precipitates! and! those! whose! isotopic!
compositions! have! been! modified! by! post'depositional! fluid! flow.! Paleo'seawater! conditions,! such!
as! oxygenation! of! the! water! body! and! seawater'freshwater! mixing! were! inferred! from! shale!
normalised! REE+Y! patterns! of! pristine! carbonates.! Redox'sensitive! elements! were! used! to! assess!
pore'water!redox!conditions!in!the!sediments.!Nd!isotopic!composition!of!shallow!water!carbonates!
were! analysed! to! deduce! the! provenance! of! the! lanthanide! source! of! the! Yangtze! Platform!
sediments.! Additionally! N! and! Cd! stable! isotope! compositions! from! organic'rich! lithologies! and!
carbonates! were! obtained! in! the! shallow! water! Xiaofenghe! section! to! infer! biological! induced!
variations!in!these!isotopic!systems.!Furthermore!we!tested!whether!Cd!isotopes!are!a!useful!proxy!
to!pinpoint!the!onset!of!biological!diversification!and!the!evolution!of!multi'cellular!life!short!before!
the!Precambrian/Cambrian!boundary.!!
!
This!dissertation!aims!to!answer!the!following!questions:!
!
I&
How& did& alteration& and& post[diagenetic& fluid& flow& affect& the& chemical& compositions& of&
Ediacaran&carbonate&rocks&of&the&Yangtze&Platform?&
&
Before! interpreting! element! concentrations! and! isotopic! compositions! in! Proterozoic!
carbonates! the! role! and! amount! of! presumable! diagenetic! overprint! of! the! studied!
lithologies!has!to!be!evaluated.!In!detail!we!try!to!test!whether!thorough!petrographic!pre'
screening!of!the!studied!samples!and!modelling!of!mixtures!of!pristine!marine!precipitates!
(deduced! from! publications! and! modern! analogues)! with! possible! fluids! overprinting! the!
carbonate!rocks!can!be!used!for!distinguishing!the!impact!of!diagenetic!alteration.!
!
II&
Are&there&systematic&differences&in&trace&element&signatures&and&isotopic&compositions&in&
shallow[&and&deep&water&sediments?&
!
!
This! is! of! particular! interest! to! understand! the! temporal! and! lateral! variations! of! the! used!
&&&&&&
!15!
!!
!
Chapter'1:'Introduction'
!
!
proxies! in! Ediacaran! carbonates.! In! detail! we! want! to! assess! the! influences! of! continental!
input! by! weathering,! riverine! inflow! and! redox! conditions! on! REE+Y,! redox! sensitive!
elements,!Sr!and!Nd!isotopes!in!marine!carbonate!precipitates.!!
!
III&
What&processes&control&REE&abundances,&patterns&and&Ce&anomalies&in&Ediacaran&shallow&
water&vs.&deep&water&carbonates?&
&
Shale! normalised! REE+Y! patterns! of! marine! carbonates! are! capable! of! recording! secular!
changes! in! marine! seawater! compositions.! Authigenic! marine! sediments! may! be! used! to!
infer!paleo!marine!conditions!in!particular!the!influence!on!freshwater/seawater!mixing!as!
well!as!the!redox!state!of!the!water!body!by!comparing!them!with!modern!analogues.!!
!
IV&
What& processes& control& the& budget& of& redox& sensitive& trace& elements& in& Ediacaran&
carbonate&rocks&from&the&deep&and&shallow&Yangtze&Platform?&
&
Many! researchers! use! redox'sensitive! trace! element! enrichments! in! organic'rich! shales! to!
infer!the!redox!state!of!the!coexisting!seawater.!However!the!distribution!of!these!elements!
in!carbonate!facies!is!poorly!understood!but!it!may!help!in!our!understanding!of!the!syn'!and!
post! sedimemtary! processes! linked! to! changes! in! the! redox! state! of! seawater! and! pore'
water!they!precipitated!out!of.!
!
V&
Can&Cd&isotope&compositions&be&used&as&a&new&proxy&for&the&onset&of&biological&innovation&
and&diversification?&
&
Stable! Cd! isotopes! are! used! in! marine! geochemistry! to! infer! nutrient! utilisation! and! bio'
productivity!in!modern!oceans.!This!geochemical!proxy!may!further!be!used!in!Proterozoic!
carbonate! rocks! to! assess! whether! biologic! fractionation! of! stable! Cd! isotopes! played! a!
significant!role!at!this!crucial!point!in!the!history!of!the!evolution!of!multicellular!life.!!
!
The!thesis!is!divided!into!six!sub!chapters.!Three!main!chapters,!each!designed!for!individual!
publication,!follow!the!introductory!chapter.!Chapter!5!is!a!conclusion!chapter!that!summarises!the!
obtained! findings.! Chapter! 6! lists! the! scientific! output! generated! by! the! author! within! the! PhD!
project.!Finally!sections!visited!during!fieldwork!in!South!China!are!listed!in!Appendix!(A!I)!and!a!brief!
analytical! protocol! is! given! for! all! measured! trace'! and! major! elements! as! well! as! the! obtained!
isotopic!compositions!in!Appendix!(A!II).!
!
16!
!!
!
Chapter'1:'Introduction'
!
!
1.4!MAIN!CHAPTERS!OF!THE!THESIS!
1.4.1.CHAPTER.2.(PUBLISHED.IN.GEOCHIMICA.ET.COSMOCHIMICA.ACTA.2015..163,.2624278).
The! focus! of! the! first! manuscript! is! to! gather! insights! in! the! processes! of! early! digenetic!
effects!on!carbonate!sediments!in!order!to!be!able!to!distinguish!primary!from!altered!geochemical!
signatures!within!the!analysed!rocks.!Therefore!the!publication!in!GCA!(Hohl!et!al.,!2015)!deals!with!
the! role! of! fluid'flow! overprint! on! deep! water! Doushantuo! carbonate! rocks! and! early! diagenetic!
effects! on! redox'sensitive! element! budgets.! Qing'Jun! Guo! from! the! Centre! for! Environmental!
Remediation,!Institute!of!Geographic!Sciences!and!Natural!Resources!Research,!Chinese!Academy!of!
Sciences,!Beijing!provided!the!sample!powders,!which!were!taken!on!a!field!campaign!in!South!China!
in!2008.!MSc!student!Stefan!Herzlieb!did!chemical!separation!work!and!assisted!in!the!analysis!of!the!
main'!and!trace!elements!and!Sr!isotope!compositions!using!ICP'MS!and!TIMS.!Some!results!of!this!
work! were! described! in! his! MSc! thesis! „Element'! und! Isotopenzusammensetzung! von!
Karbonatgesteinen!der!Beckenfazies!des!Ediacariums!der!Yangtze!Plattform!(Südchina)“.!Simon!Hohl!
carried! out! sample! analysis! and! data! reduction,! designed! the! modelling! of! fluid! overprint! on! the!
carbonates,! calculated! the! enrichment! factors! of! redox! sensitive! elements! relative! to! modern!
marine!calcite!standard!CAL'S!and!wrote!the!final!manuscript.!Harry!Becker!obtained!the!funding!for!
the!project!and!helped!in!discussing!the!data!and!revising!the!manuscript.!
!
1.4.2.CHAPTER.3.(MANUSCRIPT.SUBMITTED.TO.PRECAMBRIAN.RESEARCH).
The! second! manuscript! deals! with! the! influence! of! freshwater! influx! on! a! shallow! water!
platform! environment! and! the! resulting! trace! element;! Sr! and! Nd! compositions! in! carbonate!
leachates.!The!main!Collaborator!in!this!project!was!Shao'Yong!Jiang!from!the!State!Key!Laboratory!
of! Geological! Processes! and! Mineral! Resources,! Faculty! of! Earth! Resources,! China! University! of!
Geosciences,! Wuhan! who! organised! the! fieldwork! and! helped! in! the! collection! of! the! analysed!
carbonate!samples.!Further!he!and!his!team!(Jing'Hong!Yang!and!Hai'Zhen!Wei)!at!the!laboratory!for!
Mineral!Deposits!Research,!Department!of!Earth!Sciences!at!Nanjing!University!helped!in!analysing!
the!Nd#isotopic#compositions#using#MC#ICP'MS.$Antonia$Gamper$of$Museum$für$Naturkunde$Berlin,$
Leibniz!Institute!for!Evolution!and!Biodiversity!Science,!Berlin!helped!in!analysing!the!organic!carbon!
isotope!compositions!and!total!organic!carbon!concentrations!of!the!studied!lithologies,!while!Uwe!
Wiechert!provided!carbon!and!oxygen!isotope!measurements!in!carbonates!at!his!laboratory!at!the!
Institute! for! Geosciences! at! Freie! Universität! Berlin.! Simon! Hohl! was! responsible! for! sample!
!
&&&&&&
!17!
!!
!
Chapter'1:'Introduction'
!
!
preparation,! chemistry,! data! analysis! and! reduction! and! wrote! the! manuscript.! Harry! Becker!
organised!the!funding!for!the!sample!selection!in!South!China,!the!trace'!and!major!element!analysis!
at! Freie! Universität! Berlin! as! well! as! for! the! research! stay! at! Nanjing! University! (spring! 2013)! for!
analysing!Nd!isotope!compositions.!Furthermore!he!helped!in!interpretation!of!the!data!and!revised!
the!manuscript.!
!
1.4.3.CHAPTER.4.(UNPUBLISHED.MANUSCRIPT).
The! third! manuscript! tries! to! further! enlarge! the! isotopic! toolbox! for! pinning! the! onset! of!
Ediacaran!animal!evolution.!We!used!Cd!stable!isotopes,!a!new!geochemical!tracer!and!present!the!
first!Cd!isotope!dataset!for!Neoproterozoic!carbonates.!The!purpose!of!this!manuscript!is!to!answer!
if!modern!biological!fractionation!of!Cd!isotopes!(presumably!controlled!by!biological!uptake!within!
the!Cd!anhydrase!enzyme)!was!already!present!in!the!Ediacaran.!Steven!J.!Galer!helped!in!setting!up!
a!method!for!separation!of!Cd!in!carbonates!and!the!analysis!of!spiked!samples!using!TIMS!at!Max!
Planck! Institut! für$ Chemie,$ Mainz.$ Antonia$ Gamper$ of$ Museum$ für$ Naturkunde$ Berlin,$ Leibniz$
Institute!for!Evolution!and!Biodiversity!Science,!Berlin!helped!in!analysing!the!organic!carbon!isotope!
compositions!and!total!organic!carbon!concentrations!as!well!as!the!N!isotopic!composition!of!the!
studied!lithologies.!Simon!Hohl!did!the!chemical!separation!and!assisted!during!the!measurement!of!
Cd! isotopes! at! Max! Planck! Institut! für! Chemie,! Mainz.! He! interpreted! the! data! and! wrote! the!
manuscript.! Harry! Becker! provided! funding! for! two! trips! to! Mainz,! helped! discussing! the! obtained!
results!and!revised!the!manuscript.!!
!
!
!
18!
!!
!
Chapter'1:'Introduction'
!
!
1.5!REFERENCES!
!
Anbar,!A.D.,!Knoll,!A.H.,!2002.!Proterozoic!Ocean!Chemistry!and!Evolution:!A!Bioinorganic!Bridge?!
Science!297,!1137–1142.!doi:10.1126/science.1069651!
Ader,!M.,!Sansjofre,!P.,!Halverson,!G.P.,!Busigny,!V.,!Trindade,!R.I.F.,!Kunzmann,!M.,!Nogueira,!A.C.R.,!
2014.! Ocean! redox! structure! across! the! Late! Neoproterozoic! Oxygenation! Event:! A! nitrogen!
isotope!
perspective.!
Earth!
and!
Planetary!
Science!
Letters!
396,!
1–13.!
doi:10.1016/j.epsl.2014.03.042!
Ben!Waggoner,!2003.!The!Ediacaran!Biotas!in!Space!and!Time.!Integrative!and!Comparative.!Biology!
43,!104–113.!doi:10.1093/icb/43.1.104!
Bjerrum,!C.J.,!Canfield,!Donald!E,!2011.!Towards!a!quantitative!understanding!of!the!late!
Neoproterozoic!carbon!cycle.!PNAS!108,!5542–5547.!doi:10.1073/pnas.1101755108!
Canfield,!D.E.,!Poulton,!S.W.,!Knoll,!A.H.,!Narbonne,!G.M.,!Ross,!G.,!Goldberg,!T.,!Strauss,!H.,!2008.!
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&&&&&&
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!21!
Chapter2:AlterationofEdiacarancarbonates
CHAPTER2
MULTIPROXY
CONSTRAINTS
ON
ALTERATION
AND
PRIMARY
EDIACARAN DEEP WATER CARBONATE ROCKS,
YANGTZEPLATFORM,SOUTHCHINA
COMPOSITIONS OF
SimonV.Hohl1,HarryBecker1,SteffenHerzlieb1,QingjunGuo2
1
Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, D12249Berlin,Germany
2
Center for Environmental Remediation, Institute of Geographic Sciences and Natural
ResourcesResearch,ChineseAcademyofSciences,Beijing100101,China
2.1ABSTRACT
Theoccurrenceofshallow-anddeepwatersedimentaryfacieshasestablishedthe
Yangtze Platform in South China as a key site for the study of Neoproterozoic ocean
oxidationandEdiacarananimalevolutionfollowingtheMarinoanglaciation.TheYanwutan
section in Hunan Province is one of the few coherent sections on the Yangtze Platform
where Ediacaran deep water carbonate sediments (predominantly dolostones) are
preservedtogetherwithorganiccarbon-richshales.Herewepresentnewmajor-andtrace
element abundance data as well as Sr-, O- and C- isotope compositions of leachates from
carbonatesoftheDoushantuoformation.Weevaluatetheroleofdiageneticmodificationof
thecarbonaterocksandconstraintheredoxevolutionofEdiacaranseawaterinspaceand
time. 87Sr/86Srsystematicallyvarieswithδ18Ocarb,Sr-andBaabundances,indicatingvariable
but mostly strong modification of fluid-mobile elements by continental basin fluids. In
contrast,REE+Ypatternshavepreservedseawater-likecompositions.Capdolostones(unitI)
ontopoftheNantuodiamictitesdifferfromcapdolostonesatshallowwatersectionsonthe
Yangtze Platform in that they show no Ce-anomalies, and little alteration near the top
(87Sr/86Sr = 0.70775, δ18O = -4, δ13Ccarb = 1.1), suggesting that δ13Ccarb and δ18O of cap
dolostones at many other sections were compromised by hydrothermal alteration. The
22
Chapter2:AlterationofEdiacarancarbonates
overlyingorganiccarbonpoormicriticdolostone(unitII)showsnegativeCe-anomaliesthat
disappeartowardsthetopoftheunit.NoCe-anomaliesoccurinsubsequentorganiccarbonrich muddy dolostone units (units III to IV). These observations, enrichments in TOC that
correlate with variations in redox-sensitive metals in the carbonates, negative δ13Ccarb in
units II to IV and the decoupling of δ13Ccarb from δ13Corg argue for the existence of mostly
anoxic deep water at the Yangtze passive continental margin during the Ediacaran. The
negativeCe-anomaliesatthebaseofunitII(withnegativeδ13Ccarb)mayreflectfluctuations
towards suboxic or oxic conditions or an allochthonous origin of this unit. However, trace
metal enrichments in carbonates of the same unit argue for reducing conditions in porewater, whereas the carbonates may have preserved the REE+Y signatures inherited from
suboxic-tooxicseawater.Thetraceelementandnegativeδ13CcarbvaluesinunitsIItoIVare
consistent with a stratified basin model with a large partially remineralised organic matter
reservoirinanoxicbottomandpore-waters.
2.2INTRODUCTION
This is a postprint of a published article, due to copyright regulations the full text
article can not be published open source and is available online under
http://dx.doi.org/10.1016/j.gca.2015.04.037
23
Chapter4:CdisotopevariationsinEdiacarancarbonates
CHAPTER3
Secular changes of water chemistry in shallow water Ediacaran
ocean: Evidence from carbonates at Xiaofenghe, Three Gorges
area,YangtzePlatform,SouthChina
Simon V. Hohl1, Harry Becker1, Antonia Gamper2, Shao-Yong Jiang3,4, Uwe Wiechert1, Jing-Hong
Yang4,Hai-ZhenWei4
1
InstitutfürGeologischeWissenschaften,FreieUniversitätBerlin,Germany
2
MuseumfürNaturkundeBerlin,LeibnizInstituteforEvolutionandBiodiversityScience,Berlin,
Germany
3
StateKeyLaboratoryofGeologicalProcessesandMineralResources,FacultyofEarthResources,
ChinaUniversityofGeosciences,Wuhan430074,China
4
StateKeyLaboratoryforMineralDepositsResearch,DepartmentofEarthSciences,Nanjing
University,Nanjing210093,China
3.1ABSTRACT
EdiacarancarbonatesfromtheshallowwatersectionnearXiaofenghe(ThreeGorgesarea,
Hubei Province) on the Yangtze Platform, South China have been studied to understand post
Marinoanchangesinseawaterchemistry.Major-andtraceelementabundancesandSr-Ndisotopic
compositions were obtained on acetic acid leachates of carbonates from both the Doushantuo
Formation(MembersD1-4)andtheoverlyingDengyingFormation.CandOisotopiccompositionsof
thesecarbonatesampleswerealsoanalysedusingconventionalphosphoricacidmethod.Withthe
exceptionoftheD1capcarbonates(87Sr/86Sr=0.7088to0.713),mostsamplesshowlowMn/Srand
87
Sr/86Srsimilartoseawatervalues(0.7078inD2-D4and0.709inDengying)inferredfromEdiacaran
carbonateselsewhere.Thesedata,togetherwiththeabsenceofacorrelationbetween 87Sr/86Srand
δ18Ocarb, indicate minor diagenetic fluid overprinting. The initial εNd values of the carbonate
leachates show a limited variation range from -4.3 to -7.5 with the highest values in D1, which
overlapwiththepublisheddataforDoushantuosedimentsinSouthChina,andpossiblyindicatean
59
Chapter4:CdisotopevariationsinEdiacarancarbonates
isotopicallyhomogenousNdsourceinthesourceareaduringmostoftheEdiacaran.D1samplesof
capcarbonatesdisplaynegativeδ13Ccarbvaluesof-2.0to-3.6(VPDB)andδ18Ocarbvaluesrangingfrom
-6.5 to -7.3 (VPDB), whereas the overlying D2 strata show positive δ13Ccarb values around 6.
CarbonaterocksfromD3andD4showalargevariationrangeofδ13Ccarbfrom-1.4to9.4,withsome
samples having unusually high δ13Ccarb values coupled to low TOC contents. Most carbonate
leachates at the base of the Doushantuo display variable HREE enrichment (Pr/Yb <1) similar to
modern seawater signature and show superchondritic Y/Ho. This suggests evolution of seawater
chemistrytomodernopenoceanconditionsatthebeginningoftheEdiacaran,whereaslowerY/Ho
in D3 correlate with flat REE+Y patterns, indicating a continuously change to freshwater-seawater
mixingandsuppressionofHREE/LREEfractionationasinmodernestuaries.Carbonaterocksamples
fromD4arerichinclayminerals(upto15%),suchasnontroniteandsaponiteofpossiblyauthigenic
origin. A formation of these clay phases may only be possibly under extreme alkaline and saline
conditions.TheD4carbonateleachatesshowthehighestY/HoandlowestCe/Ce*valuesandhave
unusually high δ 13Ccarb values, which may also support the conditions of extreme shallowing and
perhapstemporarilyrestrictedbasinsthatledtoariseinsalinityduetohighevaporationrates.Ce
anomalies in carbonate leachates show strong variation throughout the profile and a secular
increase of sewater oxygenation through the Ediacaran is not obvious. However the most
pronouncedCeanomaliescanbefoundintheupperDoushantuo(Ce/Ce*aslowas0.64).
3.2INTRODUCTION
Thisisapostprintofapublishedarticle,duetocopyrightregulationsthefulltextarticlecan
not
be
published
open
source
and
is
http://dx.doi.org/10.1016/j.precamres.2015.09.006
60
available
online
under
Chapter4:CdisotopevariationsinEdiacarancarbonates
Chapter4
CADMIUMISOTOPEVARIATIONSINNEOPROTEROZOICCARBONATES-ATRACER
FORREDOXPROCESSESANDWATERMASSMIXING?
S.V.Hohl1,S.J.Galer2,A.Gamper3andH.Becker1
1
InstitutfürGeologischeWissenschaften,FreieUniversitätBerlin,Germany
2
Max-Planck-InstitutfürChemie,Abt.Klimageochemie,Mainz,Germany
3
Museum für Naturkunde Berlin, Leibniz Institute for Evolution and Biodiversity Science, Berlin,
Germany
4.1ABSTRACT
TheuseofCdisotopesasproxyformodernoceannutrientutilisationbyphytoplanktonhas
become an important tool in marine geochemistry. Of particular interest is the applicability of Cd
isotopesastracerofpastmarinebio-productivity.However,thedetailedfractionationprocessesof
Cdisotopesinthemarinerealmarestilldebated.MoststudiesfavoursubstitutionforZnatomsin
carbonicanhydraseofdiatomsasthemaindriverforthefractionation.Cdisotopiccompositionsof
leachatesofEdiacaranshallowwatercarbonatesedimentsandNandCisotopiccompositionsfrom
theXiaofenghesectionontheYangtzePlatform,S-Chinahavebeendetermined.Thedata,obtained
byusingdoublespikemethodandTIMS(ε112/110CdrelativetoNISTSRM3108,externalprecision:±
8ppm) show εCd of +0.06 to +1.07 in the cap carbonates and in the lower Doushantuo, but
significantlylightervalues(-3.53to-0.79)intheoverlyingDoushantuoandDengyingstrata.Neither
Cd concentrations, nor isotopic compositions correlate with P or Zn abundances. Given the
experimentally derived αCaCO3-Seawater of 0.99955 for the fractionation of Cd into calcium carbonate,
seawaterinequilibriumwiththesecarbonatesshouldhaveεCdbetween0.97and5.57,whichisin
therangeofmodernsurfacewater.HoweverthetrendtolowervaluesintheupperEdiacarandoes
notrepresentthesignalexpectedforincreasedbio-productivityasproposedfortheEdiacaran.The
120
Chapter4:CdisotopevariationsinEdiacarancarbonates
upper Doushantuo displays substantial fluctuations of Y/HoPAAS, Pr/SmPAAS, N and C isotopic
compositions, presumably caused by mixing of seawater with freshwater masses. Carbonates with
negativeεCdinthispartofthesectionshownegativeCe/Ce*anomaliesandhighδ13Ccarb,whichmay
indicate carbonate precipitation in shallow oxic water subjected to increased evaporation and
variable salinity. Our data suggest that the variations in the Cd isotope composition of Ediacaran
carbonates at Xiaofenghe are most likely a result of kinetic fractionation of Cd into inorganic
carbonates.IntheupperpartoftheDoushantuo,variationsmaybecontrolledbysalinitywhereasin
post-Marinoancapdolostones,sulfidicporewaterconditionsratherthanbio-productivitymayhave
producedheavyCdisotopiccompositions.
4.2INTRODUCTION
The ocean at the end of the Proterozoic Era underwent some of the most remarkable
chemical and biological transitions in Earth’s history, such as the appearance of animal life (Knoll,
2015),majorvariationsinsulphurandcarbonisotoperecords(KaufmanandKnoll,1995;Halverson
andHurtgen,2007)andindicationsforthetransitionfromananoxictoapartialoxygenateddeeper
ocean(Planavskyetal.,2010).
TheYangtzePlatform,SouthChinaisamongthemostpromisingareasintheworldtostudy
thebio-geochemicalchangesduringtheEdiacaranperiodattheendoftheNeoproterozoic.Marine
sediments of the Doushantuo and Dengying Formations cover the critical time span from the
terminationofthelastCryogenianiceage(theMarinoanglaciation)tothePrecambrian/Cambrian
boundarywiththeappearanceofthefirstmacroscopicfossilssuchasmulticellularalgae(Xiaoetal.,
2012)andtheemergenceofanimals(Yinetal.,2007;Lietal.,2008).
Inthepast,nitrogenisotopiccompositionsinmarinesedimentsprovidedinsightsintopast
oceanredoxconditionsandnitrogenbiogeochemicalcycling.Nitrogenisanessentialmacronutrient
forthelivingbiomassandtherecyclingofnitrogenspecies(e.g.NO3-,NH4+)inthewatercolumnis
strongly dependent on reduction-oxidation reactions (Ader et al., 2014).However, a problem with
the application of N isotopes in Precambrian sediments may be its post-depositional modification
(e.g.bypreferentialvolatisationof15Nfixedammonium(BeboutandFogel,1992,Aderetal.,2014)).
Therefore the use of another bio-available isotopic system is of great importance for ancient
sediments.
121
Chapter4:CdisotopevariationsinEdiacarancarbonates
Stable isotopic fractionations of Cd are another new, and not yet widely used, proxy for
marinenutrientcyclesinwater(Lacanetal.,2006;Rippergeretal.,2007;Abouchamietal.,2011)
andmarinesediments(Schmitt,etal.,2009a;Horneretal.,2010).However,theoldestsediments
analysed on their Cd isotopic compositions only date back to the Permian (Georgiev et al., 2015).
Several authors have proposed that in the aftermath of the Neoproterozoic Marinoan glaciation,
bio-productivityintheshallowEdiacaranoceanincreaseddramatically.Thepurposeofthisworkis
toevaluateifCdisotopesinshallowwatercarbonatesedimentscanbeusedasapaleo-productivity
proxyduringtheEdiacaranandtoextendtheCdisotoperecordbackintotheNeoproterozoic.
Cadmiumconcentrationsinseawatershowanutrientlikebehaviourwithsurfacedepletion
anddeepwaterenrichmentandmimicconcentrationpatternsofthemacronutrientphosphorous
(Boyleetal.,1976).Thedetailsoftheprocessesleadingtonutrient-likebehaviourofCdinmodern
seawaterremaindebated.UtilizationofCdinmarinephotosyntheticorganismsisthemostfavoured
explanation,becauseitleadstoadepletionofthesurfacewaterCdpool(Lacanetal.,2006).Asthe
maindriverfortheCduptakePriceandMorel(1990)describedavariationoftheenzymecarbonic
anhydrase,whichisactiveintheresorptionofcarbondioxideduringphotosyntheticprocesses.The
Cdincorporatingcarbonicanhydrasehassofaronlybedescribedfromdiatoms(Xuetal.,2008).
RecentpublicationsshowedthatCdconcentrationpatternsmirrormajorvariationsintheir
isotopic compositions (Ripperger et al., 2007; Schmitt, 2009a; Abouchami et al., 2011)). The data
usually exhibit Cd depleted surface waters with isotopically heavy compositions and deep waters
show higher Cd concentrations and lighter isotopic compositions, presumably reflecting surface
removal of light isotopes by marine photosynthetic organisms and their decomposition and remineralisationindeepwaters(Lacanetal.,2006;Rippergeretal.,2007).
4.3GEOLOGICBACKGROUND,SAMPLESELECTIONANDMETHODS
The Xiaofenghe section (Hubei Province, South China) is situated 30 km NE of the Three
GorgesDamanddevelopedontheS-SEfacingpassivemarginoftheYangtzecraton(WangandLi,
2003). The section comprises of dolomite- and calcit bearing carbonate sediments and mudstones
fromtheDoushantuoandoverlyingDengyingFormationandisdescribedinliteraturetohavebeen
depositedunderveryshallowwaterorevenlagoonalconditions(VernhetandReijmer,2010;Xiaoet
al.,2012).
122
Chapter4:CdisotopevariationsinEdiacarancarbonates
The section has been sampled in detail with the aim to determine in detail geochemical
variationsincarbonatesedimentsamplesandtostudytheroleofalterationandthepreservationof
primarycompositions.Thesampledrockswerepre-screenedbymicroscopeandSEMforalteration
structures, such as calcitic veins or weathering fronts, cleaned and powdered. Major- and trace
element compositions of acetic acid leachates and Sr-Nd-Ccarb-Ocarb isotopic compositions were
reportedinHohletal.(submitted).
Stableisotoperatiosandconcentrationmeasurementsofnitrogenandorganiccarbonwere
obtained using a Thermo-Finnigan MAT V isotope ratio mass spectrometer coupled to a Thermo
Flash EA 1112 elemental analyser via a Thermo/Finnigan Conflo III-interface at the Museum für
Naturkunde Berlin. δ15N analyses were performed on the bulk rock powder whereas for δ13Corg
measurementssamplepowdersweredecalcifiedusing2MHCl.Isotopicratiosareexpressedinthe
conventional delta notation relative to AIR and the V-PDB (Vienna PeeDee Belemnite) standard,
respectively.Thestandarddeviationforrepeatedmeasurementsofalaboratorystandardmaterial
(peptone)isgenerallybetterthan0.2‰forbothisotopicsystems.AftersamplecombustionaCO2trap was used to reduce interferences between bulk rock nitrogen and carbon isotope signals.
δ13Ccarb of Xiaofenghe carbonates was obtained using standard methods at Freie Universität Berlin
andweredescribedbyHohletal.(submitted).
For Cd isotope analysis we reacted 1 g of sample powder in pre-cleaned 50 ml centrifuge
vialswith50mlof1MaceticacidbufferedtoapHof5.Samplesreactedundercontinuousrotation
overnight, then were centrifuged and pipetted. A 106Cd – 108Cd spike was added to aliquots of the
samplescontaining~100ngCd,followingtheproceduresdescribedinSchmittetal.(2009b).After
equilibrationwiththespike,0.6mlof8.5MHBr/10mlsamplewereaddedtoobtainaconcentration
of~0.5MHBr.TheCdseparationandpurificationwasachievedbyusingatwo-stepseparationon
Biorad Polyprep columns filled with 200 µl of Bio Rad AG1-X8, 100-200 mesh in nitric form and
elutionwith0.25NHNO3.ThesampleswerethenloadedontosingleRefilamentsandcoveredwith
1 µl silica gel activator. Cd Isotopic compositions were determined using a Thermo-Fisher Triton
Thermal Ionisation Mass Spectrometer (TIMS) at the Max Planck Institut für Chemie in Mainz. The
rawdatawascorrectedofflineforinternalinstrumentmassfractionationusingtheexponentiallaw.
FollowingAbouchamietal.(2012)Cdisotopedatawereexpressedasε112/110Cdvalues(deviationsof
112
Cd/110Cdinpartsper10,000fromareferencematerial):
! !!"
!!"
!"=
!!"!" !!"!"
!!"!" !!"!"
!"
!"#$%&
− 1 x104
123
Chapter4:CdisotopevariationsinEdiacarancarbonates
Asreferencematerial(RM)weusedthenowwidelyacceptedNISTSRM3108Cdstandard
(Abouchami et al., 2012). The Cd concentrations have been obtained by isotope dilution and have
combinedanalyticaluncertaintiesoflessthan0.1%.
4.4RESULTS
ε112/110CdinthreecapcarbonatesofXiaofengherangesbetween-0.056±0.62and-0.455±
0.23. The Cd concentrations in the same member vary between 0.2 and 0.62 µg/g showing no
correlationwiththeisotopiccompositions.Incontrast,ε112/110CdinthemiddleDoushantuois+1.069
± 0.35 and -3.625 ± 0.11 close to the top of the Formation. The Cd isotopic data show a trend to
lighter values up section. Cd concentrations range between 0.093 and 2.507 µg/g and show no
systematic variation with isotopic composition or stratigraphic position. ε112/110Cd values of two
analysedDengyingsamplesare-2.546and-2.19with0.14µg/gand0.1µg/gCdrespectively.
Capcarbonatestratashowδ13Corgdatawithanaveragevalueof-27‰.δ15Ncompositions
decrease upwards from 2.6 ‰ to 0.5 ‰. Throughout overlying strata of the lower Doushantuo
Formation δ13Corg values remain relative invariant ranging around ~-28 ‰ before they decrease
down to -33.8 ‰ in black shales of the middle Doushantuo Formation (~103.0 m). TOC values
steadilyincreasefrom~0.1%strataoverlyingthecapcarbonatetoamaximumvalueof1.105%in
stratacomprisingblackshales(102.7m).δ15Ncompositionsaswellincreasetoanaveragevalueof
~4.5 ‰, however showing a wide range from 1.9 ‰ to 6.6 ‰. Thereby, the black shale shows
constant15N-enrichedisotopecompositionsof~5‰.
Lime-anddolostonesofthemiddleDoushantuoFormationaredominatedbyδ13Corgvalues
fluctuating around ~ 28 ‰ whereas TOC values decrease down to an average value of 0.09 % in
strata comprising dolostones of the middle Doushantuo (~170 m). Strata overlying the black shale
showδ15Ndatastabilisingaround4‰.
124
Chapter4:CdisotopevariationsinEdiacarancarbonates
FIG .4.1
a-c)CompiledorganicandinorganiccarbonisotopedatafromHohletal.,(2015inreview).Instead
of stratigraphic height, sample numbers are indicated on the y-axis for better resolution of the
variations.
d)ε112/110Cdofcarbonateleachates(relativetoNISTSRM3108Cdstandard);redlinerepresentsCd
concentrations in µg/g; (*) dashed blue line represents the calculated isotopic composition of
seawaterforinorganicequilibriumprecipitationofcalcitefollowingHorneretal.(2011).
e)Bulkrockδ15N(relativetoAir)andconcentrationsofNitrogeninwt.%(greenline).
f)ShalenormalisedY/HoratiosincarbonateleachatesfromHohletal.(2015–inreview);dashed
linerepresentsmodernseawaterafterBauetal.(1995).
Δ13Ccarb-org values range from 22.9 (in the basal Doushantuo Formation) up to 37.6 in the
middleDoushantuoFormation(Fig.4.1).
δ15N values of Doushantuo cap carbonates vary between 0.5 and 2.6 whereas in middle
Doushantuotheyliebetween1.9and6.6‰.ThedataontheupperDoushantuoFormationshow
fluctuationsinδ15Ncompositions,wheretherespectivelightδ15Nvaluesoccurinsampleswithlow
125
Chapter4:CdisotopevariationsinEdiacarancarbonates
Nconcentrationsinthebulkrockandmaythusbeananalyticalartefactortheresultofdiagenetic
modificationoftheprimaryisotopicsignal(Fig.4.1).
4.5DISCUSSION
Phytoplankton utilisation of Cd may be the major process controlling the variations in
modernseawaterCdbudgets(PriceandMorel,1990;Lacanetal.,2006;Rippergeretal.,2007).As
organically bound Cd is the major removal process of Cd in modern marine systems, ancient
carbonate sediments could be an important archive for determining nutrient cycles in ancient
seawater (Horner, Rickaby and Henderson, 2011). If this process was active in the late
Neoproterozoic,itgivesnewinsightsintoprocessesleadingtotheevolutionofmulticellularlifeat
thePrecambrian/Cambrianboundary.Howeverarangeofotherprocessesmayaffectthevariability
of Cd concentrations and isotopic compositions in ancient marine sediments. Therefore when
analysingCdconcentrationsandisotopiccompositionsinancientmarinesediments,theinfluenceof
additional fractionation processes must be evaluated. The range of Cd isotope fractionations in
carbonate leachates from Xiaofenghe section is larger than 4 ε112/110Cd units and cannot be
explained by analytical artefacts as the observed variations change systematically throughout the
profile(tolightervaluesatthetopofthesection).
4.5.1INFLUENCEOFTERRESTRIALINPUT
Fractionation of Cd isotopes in detrital minerals is reported to be at least one order of
magnitude smaller than variations in seawater (< 2 ε112/110Cd vs. 20 ε112/110Cd (Wombacher et al.,
2003), hence the variation in Cd isotope data from Xiaofenghe section (> 4 ε112/110Cd) exceeds the
isotopicvariationinloesssamples(Schmittetal.,2009a).DatafromXiaofengheshownocorrelation
ofCdconcentrationsorisotopecompositionswithKandAlcontentsinaceticacidleachatesortotal
claycontentsinbulkrockassemblages,thereforetheroleofdetritalCdinputbymaybenegligible.
4.5.2DIAGENESIS
LatefluidflowoverprintistypicalforPalaeozoiccarbonatesfromSouthChinaandmayhave
alteredtheCdisotopecompositions.Hohletal.(submitted)haveshownthat,withtheexceptionof
thecapdolostones,carbonaterocksatXiaofenghewerenotaffectedmuchbylate-stagefluidflow
126
Chapter4:CdisotopevariationsinEdiacarancarbonates
(as indicated by their 87Sr/86Sr and δ18O data) and thus, their trace element budgets presumably
reflectthepartitioningandincorporationfromEdiacaranseawater.ε112/110Cdvalues>zeroreference
standard correlate with light carbon and oxygen isotopic compositions (Fig. 4.3). These “heavy”
values are only abundant in the basal Doushantuo samples, which also have Mn/Sr ratios > 5,
commonlyusedasdenominatorformeteoricfluidoverprint(BrandandVeizer,1980).Furthermore
the samples have the lowest Cd and N concentrations, suggestive of preferential leaching of the
elements from these samples. If Cd concentrations in the cap dolostones were modified by
dissolution processes this could have led to removal of light Cd isotopes at the base of the
Doushantuo.
4.5.3POSSIBLECDFRACTIONATIONEFFECTSTOBETESTED:
4.5.3.1BIOLOGICALFRACTIONATION
δ13Ccarb values at Xiaofenghe suggest a deposition under shallow water marine conditions
fractionationofcarbonisotopesbyphytoplanktonabovethecapdolomites(Hohletal.,submitted).
Severalauthorshavefavourednutrient-likeuptakeofCdintophytoplanktonasthemaindriverfor
Cdisotopefractionationofmorethan18ε112/110Cdunitsinmodernoceans(Rippergeretal.,2007;
Abouchamietal.,2014).Howeversofaronlyonespecificenzymeindiatoms(Cdcarbonicanhydrase,
(Xu et al., 2008)) has been identified as being capable of incorporating the toxic metal Cd into
phytoplankton. Horner et al. (2013) suggested that nonspecific uptake of Cd into planktonic
organismsmayleadtosubsequentstorageofCdinthecellmembraneofplanktonicorganisms.Both
uptakeprocessesofCdintoorganicmatterwillleadtoadepletionoflightCdinthephoticzoneand
heavy Cd isotope enrichment in the deeper parts of the water column. Under closed system
conditions(e.g.arestrictedbasin)carbonatesprecipitatinginanincreasingproductiveenvironment
towardstheCambrianshouldyieldheavierisotopiccompositions.
δ13Corg values throughout the section agree with previously published data from the
Doushantuo Formation (e.g. Ishikawa et al., 2013) and display values characteristic for marine
phytoplankton. Although presumably deposited under very shallow- and photic conditions, the
carbonateleachatesrevealnotrendtoheavierε112/110Cdcompositionsup-section.ε112/110Cdvalues
dropabovethebasalDoushantuocapdolomites,behavingoppositetoincreasingδ13Ccarbvalues.
ε112/110Cd values show no correlation with δ15N. However, the curves of the two isotope
systems match in some parts of the section. Whereas Cd isotopic compositions are higher in the
127
Chapter4:CdisotopevariationsinEdiacarancarbonates
basal Doushantuo cap dolomites, corresponding nitrogen isotopic compositions show low but
positiveδ15Nvalues.Thelownitrogenisotopecompositionofcapcarbonatestratasuggestsstrong
N2-fixation by diazotrophs in the euphotic zone (Sachs and Repeta, 1999). Such scenarios (e.g.
cyanobacterial blooms) are often documented from redox-stratified oceanic basins (e.g. in the
modernBalticSea)(Strucketal.,2004;Plougetal.,2010).
Elevated δ15N vales up to 6.6 of strata comprising the lower and middle Doushantuo
Formation hint towards a shift in the nutrient regime to a NO3- dominated marine environment
(Ader et al., 2014). Nitrogen isotope data imply, that NO3- became the predominantly utilised
nutrientforprimaryproducerswhileN2partlyremainedunusedinsurfacewaters.Thiscanpossibly
be attributed to increased oxygen availability that is essential to allow remineralisation of organic
mattervianitrification-denitrificationinteractions(Canfieldetal.,2010,Ader2014).Therefore,δ15N
datashowthatnitratewasstableintheshallowwaterduringtheearlyandmiddleDoushantuoand
thusintermediatewatersmusthavebeenatleastmildlyoxygenated(Aderetal.,2014).Theseoxic
to subocic conditions in were further indicated by negative Ce anomalies recorded in carbonate
leachatessofthesamemember(table4.1).
The upper Doushantuo shows fluctuations in the nitrogen isotope signature and a drop in
δ15Ndownto0.2,whichbroadlymirrorfluctuationsintheε112/110Cdandδ13C(organicandcarbonate)
andmayimplyfluctuationswithrespecttothestabilityofnitrateduetochangingoxygenlevels.
4.5.3.2REDOXCONTROLLEDFRACTIONATION
Recent work by Gorgiev et al. (2015) highlighted aspects of redox controlled Cd
concentrationsandisotopiccompositionsinmarinesediments.Cdisanotaredox-sensitiveelement
and only present in 2+ state but Cd bound on organic matter (OM) will be enriched in anoxic
sedimentswhereOMoxidationisinhibited.UndereuxinicconditionsCdmayalsohavebeenbound
intosulphides(CdS)contributingtosedimentaryCdenrichmentsinoxygenminimumzones(Janssen
et al., 2014). OM and/or sulphide-rich sediments would show higher Cd concentrations and
potentially lighter isotope composition than the remaining seawater as both OM and Cd-bearing
sulphidespreferentiallyincorporatelighterCdisotopes(Schmitt,etal.,2009a).
Mnenrichmentfactorsinthecarbonateleachates(relativetotheMnconcentrationinthe
Phanerozoic calcite standard CAL-S) show a positive correlation with ε112/110Cd (Fig. 4.3). As Mn in
modernoxicsurfacewatersisincorporatedintoMn-oxidesandhydroxidesanenrichmentofMnin
128
Chapter4:CdisotopevariationsinEdiacarancarbonates
thecarbonatephasesmayreflectreductiontoMn2+duringanoxicpore-water-sedimentinteractions
(Thomson et al., 1986). Whole rock organic matter contents vary strongly within the profile and
neithercorrelatewithMnconcentrationsinthecarbonateleachatesnorwithε112/110Cd.
FIG .4.2
BSD picture of a Xiaofenghe
sectioncapdolostoneat2.36m
stratigraphicheight.Thesample
shows calcitic fillings within a
porous dolomicritic matrix.
Subhedral to euhedral (10 - 40
µm diameter) sulphide grains
are abundant in samples of the
basal
Doushantuo
cap
carbonates.
The basal Doushantuo cap dolomites reveal Mn enrichments and positive fractionated
ε112/110CdatlowCdconcentrations.Furthermoresubhedral10-40µmsulphidegrainsareabundant
inthesesamples(Fig.4.2).AlthoughCe/Ce*ratios<0.9(Hohletal.,submitted)suggestthatduring
cap dolomite precipitation surface waters on the Yangtze Platform were already suboxic to oxic.
However,pore-waterconditionsmayhavebeenanoxic,leadingtotheprecipitationofsulphidesand
Mn-richcarbonates.FramsonandLeckie(1978)showedthatundersulphidicconditionslabileCdcoprecipitates with sulphides. The effect of authigenic sulphide formation on the fractionation of Cd
isotopes within anoxic marine sediments is poorly understood. While Wombacher et al. (2003)
found no evidence for fractionation of Cd isotopes in low temperature sulphide precipitation, the
work done by Schmitt et al. (2009a) showed that hydrothermal sulphides had distinctively lower
ε112/110Cd values than marine sediments, indicating a substantial fractionation effect of up to 4
ε112/110Cdunits.
129
Chapter4:CdisotopevariationsinEdiacarancarbonates
Preferential incorporation of light Cd isotopes into authigenic sulphides, leaving the
carbonate phases isotopically heavy, may have only affected the basal Doushantuo at Xiaofenghe.
Although middle and upper Doushantuo and Dengying carbonate leachates show co-variation of
ε112/110CdwithMnenrichments,positiveε112/110CdvaluesareonlypresentinthelowerDoushantuo.
Pore-water conditions at Xiaofenghe were most likely more oxidised after the cap dolostone
deposition as indicated by lower TOC contents and Spyrite/Corg ratios (Jiang et al., 2011; Xiao et al.,
2012).
4.5.3.3SALINITYCONTROLLEDFRACTIONATION
Whereas inorganic carbonate precipitation in saline waters leads to a constant Cd
fractionation factor of αCaCO3-Cdaq = 0.99955 ± 12 (insensitive to temperature, Mg concentration
andprecipitationrate),inorganicfreshwatercarbonatesaremostlikelyincapableoffractionatingCd
isotopes (Horner, Rickaby and Henderson, 2011b). Calculated ε112/110Cd values for seawater in
equilibrium with the carbonates analysed from Xiaofenghe section range between +0.975 and
+5.569 (blue line Fig. 4.1). Cd uptake in freshwater calcites is much faster than in saline waters,
where a decreased Cd uptake may be a result of ion blocking on the calcite mineral surface sites
(Horner, Rickaby and Henderson, 2011b). Cd isotope compositional variations within carbonate
leachates may therefore also be a result of variable salinity of the seawater at the Xiaofenghe
depositional site. If correct, the Cd isotope signal may also have been influenced by freshwaterseawatermixing.Hohletal.,(2015-submitted)showthattheXiaofenghesectionmighthavebeen
influencedbysubstantialfreshwaterinputs,whichresultedinvariableREE+Yratiosinthecarbonate
sediments.
130
Chapter4:CdisotopevariationsinEdiacarancarbonates
Y/HoPAAS > 2
Mn/Sr > 5
FIG .4.3
N wt.%
0.10
middle Doushantuo
0.05
0
30
Σ REE µg/g
Differentproxiesvs.ε 112/110Cd(relativeto
NIST SRM 3108 reference material).
Positive correlations are given with R2
value (excluding outliers in the shaded
area (YN/HoN > 2) and the diagonal
patternarea(Mn/Sr>5).
R2 0.86
20
Positive ε 112/110Cd values correlate with
high Mn/Sr ratios, very light oxygen
isotopic compositions and low N
concentrations.
R2 0.71
10
Light ε 112/110Cd values are found in
samples with low Σ REE concentrations,
high fractionation of Y over Ho, no or
minor Mn enrichment relative to
Phanerozoic calcite standard CAL-S and
less
negative
oxygen
isotope
compositions.
0
R2 0.67
YN/HoN
2.5
2.0
1.5
EF-Mn CAL-S
15
EF up to 495
10
2
R 0.84
5
0
2
R 0.67
δ18Ocarb
0
−5
−10
−3
−2
−1
ε112/110Cd
0
1
131
Chapter4:CdisotopevariationsinEdiacarancarbonates
Shale normalised REE+Y patterns of modern oxidised surface waters are characterized by
enrichment in HREE over LREE, negative Ce anomalies and superchondritic (>28) Y/Ho ratios
(ElderfieldandGreaves,1982;Bauetal.,1996;Nozakietal.,1997).Ithasbeenshownthatmarine
carbonatemineralsincorporatetheREE+Ysignaturesofcoevalseawater(WebbandKamber,2000;
Kamber and Webb, 2001; Nothdurft et al., 2004). Thus REE concentrations in carbonates can be a
usefultoolforpaleo-environmentalreconstructions.Aceticacidleachatesofcarbonaterocksfrom
Xiaofenghe section exhibit superchondritic Y/Ho ratios, however, Y/Ho ratios close to modern
surface ocean values only occur in the middle Doushantuo and at the boundary to the Dengying
Formation.StrongvariationsofY/HoPAASfrom1.5to2.5intheupperDoushantuocorrelatewiththe
negative excursions of δ13Ccarb, ε112/110Cd and δ15N. These samples also display a reversal of the
LREE/HREEfractionationfromshalenormalisedPr/Ybratiosof(downto0.31inmiddleDoushantuo
and down to 0.23 in Dengying samples (table 4.1)) to shale normalised Pr/Yb ratios > 1 in some
samples of the cap carbonates and upper Doushantuo, presumably as a consequence of a relative
LREEenrichment.
FlatshalenormalisedREE+YpatternsoccurattheboundaryofmiddletoupperDoushantuo
oftheXiaofenghesectionandoccurtogetherwithdiminishedyttriumanomalies.Thesesignalsare
unusual for open marine sediments and are similar to conditions in estuarine mixing zones
(LawrenceandKamber,2006).TheXiaofenghesamplesshowhighYN/HoNratiosinsampleswithlow
ε112/110CdvaluesandlowtotalREEconcentrations(Fig.4.3).Thematchoftheseparameterssuggests
thattemporallyincreasedinputoffreshwaterintoalagoonalenvironmentincreasedthefluxoflight
REE (therefore flattening the shale normalised carbonate leachate REE patterns, Hohl et al. (2015)
submitted), decreased the salinity of the mixed water-mass and thus supressing the Cd isotope
fractionationduringinorganiccarbonateprecipitation.
4.6CONCLUSIONS
Ediacaran carbonate leachates at Xiaofenghe show Cadmium isotope fractionation with
temporal evolution to light isotopic compositions. The variation of ε112/110Cd signals overlaps with
values reported for modern shallow seawater. However, the reasons for the fractionation of Cd
isotopes may be diverse and are most likely controlled by inorganic processes rather then by
substitution of Cd for Zn in phytoplankton. The Cd incorporating carbonic anhydrase is so far only
132
Chapter4:CdisotopevariationsinEdiacarancarbonates
described for Diatoms and this enzyme might not have existed in the Precambrian (since the
emergenceofdiatomsfallsintothelateCretaceous).
The fractionation of Cd isotopes in Ediacaran carbonate leachates is most likely a result of
inorganicprocessessuchasprecipitationofauthigenicsulphidesunderanoxicpore-waterconditions
in cap dolostones at the base of the Doushantuo and changes in the fractionation rate due to
variablesalinityincarbonatesedimentsoftheupperDoushantuoasaresultofseawater-freshwater
mixinginanestuarine-likeenvironment.
4.7ACKNOWLEDGEMENTS
ThisworkwasfundedasapartofDFGResearchGroupFOR736“ThePrecambrian-Cambrian
BiosphereRevolution:InsightsfromChinesemicrocontinents”(SubprojectBe1820/4-2).Wethank
Reimund Jotter and Wafa Abouchami at the Max-Planck-Institut für Chemie in Mainz for their
supportinthelabandmembersofFOR736whohelpedinsamplingtheanalysedrocksinthefieldin
SouthChina.WewouldliketothankUweWiechertforhelpwithanalysisoflightstableisotopesat
theFreieUniversitätBerlin.Weacknowledgehelpfulcommentsanddiscussiononanearlyversion
ofthismanuscriptbyMichaelTatzel.
133
Chapter4:CdisotopevariationsinEdiacarancarbonates
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135
Chapter4:CdisotopevariationsinEdiacarancarbonates
Table4.1.:stableisotopedata;NandCconcentrations;assortedshalenormalisedREEratiosandMnenrichmentsrelativetoCal-SfromHohletal.(2015b).D1-D4=DoushantuoFm.,DG=DengyingFm.
1
2
3
4
13
1
18
1
13
13
112/110
2
15 3
4
(sample
OandCisotopicdatarelativetoVPDB;
caluculatedfollowingequationsgivenbyLawrenceandKamber,2006)
Height[m]
Member
δ CcarbNrelativetoAir;
δ Ocarb δ CdrelativetoNISTSRM3108,
Corg
Δδ ε
Cd 2SE
Cd[µg/g]
δ N
N[wt.%]
TOC[wt.%]
C/N
ΣREE[µg/g]
Ce/Ce* YN/HoN
1
0.2
D1
-3.8
-6.7
-28
24.2
2
0.2
D1
-3.8
-6.7
-28
24.2
3
0.75
D1
4
1.6
D1
-3.7
-7.7
5
1.6
D1
-3.7
-7.7
6
2.3
D1
-3.8
-7.3
-26.7
22.9
7
3.85
D1
-3.2
-6.9
8
4.8
D1
-1.2
-12.3
-28.4
9
4.8
D1
-1.2
-12.3
-28.4
10
6.65
D2
12
12.1
D2
13
22
D2
25
36
D2
26
37.5
D2
33
61.5
34
-6.8
0.6
-10.4
D2
6.4
-6.0
65
D2
6.5
-6.1
35
70
D2
7.3
-3.5
36
72.5
D2
37
73.7
D2
38
75
D2
5.1
-28.1
-29
-28.3
0.1
0.46
0.23
0.028
27.2
27.2
25.4
0.29
2.51
0.006
29.6
1.07
0.35
0.028
-1.69
0.09
0.2
-29
35.5
-25.5
-4.8
-27.3
32.4
39
75.6
D2
5.4
-4.4
-26.8
32.2
40
76
D2
5.2
-4.5
-28.1
33.3
41
76.5
D2
42
77.5
D2
43
77.5
D2
44
79.5
D2
45
80.5
D2
46
81.5
D2
4.8
-5.0
-27.9
32.7
48
84.5
D2
6.1
-1.6
-28.3
49
85
D2
5.4
-4.4
-28.8
50
86
D2
51
87.2
D2
52
88
D2
53
88.7
D2
-27.2
54
89
D2
5.2
-4.0
55
90
D2
5.9
-2.5
136
6.2
-4.1
6.2
-4.1
-3.9
1.8
0.003
0.008
1.8
0.003
0.008
0.11
PrN/YbN
EFMn(Cal-S)
2.7
16
0.95
1.5
0.97
48
27
0.83
1.4
1.1
30
15
2.1
0.71
1.4
0.97
1
2.6
0.006
2.6
0.006
2.3
0.005
0.0001
0.02
0.5
0.011
0.8
0.004
0.06
4.9
0.066
0.016
0.2
13
1.2
1.5
1.05
496
2.4
0.008
0.25
32
4.9
0.84
1.4
0.85
7.8
4.2
0.011
0.12
11
2.5
1.11
1.3
0.41
8.9
2.2
0.66
1.7
0.57
2.1
1.7
0.69
1.8
0.49
2.9
1
0.85
1.7
0.47
0.06
5.1
0.014
0.21
15
5.5
0.028
0.12
4.4
3.9
0.017
3.8
4.9
0.092
-2.04
0.25
0.035
6.6
0.13
0.61
4.7
5.4
0.034
0.22
0.33
2.2
0.71
0.76
1.5
0.47
0.87
1.7
0.58
0.9
2.1
0.77
6.4
0.33
0.69
1.5
0.4
0.14
2.9
1.01
1.6
0.58
1.7
6.6
2.9
1.15
1.3
0.62
5.2
9.3
3.4
1.19
1.3
0.63
5.2
2.1
1.4
4.8
0.023
35.6
5.9
0.046
0.43
33.2
5.0
0.032
0.42
13
1.4
0.75
1.6
0.49
4.8
5.2
0.044
0.41
9.4
1.7
0.69
2.6
0.37
1.7
4.9
0.049
0.38
7.7
13
0.86
1.4
1.31
3.8
0.092
0.006
0.1
3.2
0.64
2.1
0.5
1.6
34.4
2.5
4.6
0.031
0.45
14
3.6
0.76
1.9
0.65
2.2
34.2
4.8
0.034
0.48
14
1.9
0.72
2.3
0.36
2.5
4.5
0.067
0.92
14
6.4
0.89
1.6
0.81
2.1
5.3
0.044
0.71
16
6.9
0.76
1.7
0.89
2.5
4.8
0.037
0.36
10
7.3
0.97
1.7
0.7
2.2
4.6
0.048
0.71
15
-27
32.2
6.7
0.8
1.5
0.91
1.1
34.7
0.044
-28.8
4.4
-29.4
-29.4
-27
-28.8
5.2
0.06
0.62
-25.4
0.2
0.056
-26.7
0.0
0.091
-28.6
-26.5
31.7
-30.1
0.94
Chapter4:CdisotopevariationsinEdiacarancarbonates
sample
Height[m]
Member
δ Ccarb δ Ocarb δ Corg
Δδ 56
91.2
D2
5.5
-3.3
-27.7
33.2
57
91.7
D2
6.1
-2.9
-27.6
33.7
58
92
D2
3.6
-1.2
-27.3
59
92.5
D2
60
93
D2
61
96.2
62
98
63
99
13
1
18
1
13
2SE
Cd[µg/g]
δ N
N[wt.%]
TOC[wt.%]
C/N
ΣREE[µg/g]
Ce/Ce* YN/HoN
PrN/YbN
EFMn(Cal-S)
2.3
0.017
0.29
17
5.4
0.087
0.77
8.9
1.3
0.69
2.58
0.49
2.3
3.2
1.2
1.94
0.33
2.5
3.9
0.02
1.9
0.011
0.26
23
2.4
0.72
2.3
0.57
1.4
13
ε
112/110
2
Cd 15
3
D2
-28.6
3.2
0.014
0.35
25
D2
-27.9
4.7
0.04
0.35
8.7
29
0.94
1.2
0.92
3.2
D2
-27.9
2.8
0.011
0.15
13
16
0.82
1.6
1.52
3.1
5.6
-2.6
-29.2
34.8
4.8
0.06
0.32
5.3
10
0.92
1.4
1.36
2.9
-28.6
33.9
3.9
0.019
0.65
34
3.5
0.95
1.4
0.82
3.6
2.4
0.017
0.28
16
64
99.85
D2
65
100.95
D2
66
101.5
D2
5.3
-3.4
67
101.85
D2
5.8
-2.4
68
102
D2
6.5
-1.7
69
102
D2
6.3
-1.3
-29
70
102.1
D2
71
102.4
D2
72
102.6
D2
73
102.6
D2
74
102.7
D2
75
103
D2
76
103
77
-28.7
4.3
0.95
10
-1.4
-28.8
34.5
4.5
0.097
0.4
4.1
5.6
-1.5
-32
37.6
-1.23
0.35
0.1
4.4
0.085
1
4.6
0.051
D2
6.8
-1.1
-28.1
34.9
5.3
0.14
103
D2
5.1
-2.1
-27.2
32.3
78
103.5
D3
5.4
79
103.5
D3
5.2
-3.4
80
104
D3
3.5
-2.8
81
104
D3
82
104.25
D3
-27.8
-2.2
-27.3
31.5
-4.9
-28.3
33.3
0.8
1.6
1.22
4
0.88
1.4
0.96
3.2
9.4
0.92
1.6
0.8
2.5
4.5
1.1
0.63
12
5.8
1.19
1.5
0.73
4.0
0.21
4.1
8.8
1.4
1.3
0.83
2.9
0.97
7.1
44
1.16
1.5
0.75
2.1
0.13
0.89
7.1
11
0.98
1.6
0.7
2.4
3.1
0.015
0.59
39
3.9
0.98
1.3
1.07
1.2
3.1
0.015
0.59
39
3.5
1.09
1.4
0.84
3.5
1.4
4.9
36.4
-29.2
32.7
5.0
0.029
0.11
3.9
14
1.33
1.4
1.32
-1.14
0.12
0.4
5.0
0.029
0.11
3.9
2.6
0.87
1.5
0.94
1.6
3.4
0.015
0.17
11
2.7
1.09
1.5
1
3.4
4.1
0.012
0.15
12
3.4
1.23
1.5
0.73
5.3
2.7
0.018
0.23
13
2.9
0.76
2.1
0.31
2.3
3.0
0.009
0.43
48
2.9
0.71
1.6
0.75
1.5
-29.2
83
104.5
D3
84
104.5
D3
5.0
85
105.5
D3
87
108.15
D3
-31.9
88
108.7
D3
4.0
-1.0
89
109.5
D3
2.0
-6.3
90
109.5
D3
4.9
0.039
0.21
5.5
5.7
1.08
1.5
1.2
9.5
-27.3
31.3
5.6
0.126
0.56
4.4
15
1.03
1.4
0.97
2.4
-27.8
29.8
4.6
0.013
0.13
10
8.6
1.06
1.7
1.39
34
4.6
0.013
11
0.86
1.5
1.29
4.4
-25.8
-27.8
6
12
-31.2
4.2
0.094
5.7
-31.2
4.8
0.045
-33.8
4
137
Chapter4:CdisotopevariationsinEdiacarancarbonates
sample
Height[m]
Member
δ Ccarb δ Ocarb δ Corg
Δδ 91
110
D3
3.6
-6.8
-28.6
32.2
92
110.5
D3
93
111.1
D3
2.9
-6.8
94
112.2
D3
2.8
-8.6
95
113.9
D3
6.6
-5.4
96
116
D3
6.9
97
118.5
D3
99
123.8
D3
100
13
1
18
1
13
-28.4
-29.6
13
32.5
ε
2SE
Cd[µg/g]
δ N
N[wt.%]
TOC[wt.%]
C/N
ΣREE[µg/g]
Ce/Ce* YN/HoN
PrN/YbN
EFMn(Cal-S)
4.8
0.01
0.096
9.6
14
0.94
1.7
2.59
116
5.5
0.01
0.087
8.7
16
0.86
1.6
3.24
257
5.2
0.015
0.14
9.3
11
0.97
1.5
2.23
31
3.7
0.008
8.3
0.79
1.5
2.03
74
2.7
0.007
3.5
0.69
1.7
1.83
3.6
0.01
3.0
0.7
1.8
1.23
162
112/110
2
Cd 15
3
-4.6
6.1
-6.4
-27.2
33.3
3.6
0.009
0.072
8.0
6.7
0.87
1.7
1.37
6.1
-2.3
-28.6
34.7
3.3
0.012
0.17
14.5
11
0.97
1.3
1.67
7
-31
36.4
-1.62
0.47
0.02
5.3
0.018
0.24
13.1
10
1.02
1.4
1.98
19
4.1
0.009
12
1.01
1.5
2.97
60
-30.1
4.2
0.008
0.16
20
9.0
0.87
1.4
2.21
32
4.4
0.007
0.31
44
16
0.99
1.8
1.17
2
4.0
0.007
0.13
18
11
1.01
1.5
2.3
10
5.5
0.017
12
0.86
1.1
1.04
2.1
5.9
0.048
1.6
34
1.9
0.77
2.4
0.38
0.1
2.1
0.81
2.4
0.41
0.41
125
D3
5.4
-3.2
101
130
D3
5.7
-4.9
103
133.5
D3
104
135
D3
3.7
-7.5
-29.2
32.9
105
136
D3
5.6
-6.7
-27.8
33.4
107
142
D4
-1.3
-0.9
-29.2
27.9
0.051
7.3
4
108
142.4
D4
110
152
D4
111
154
D4
9.4
-8.4
-25.9
35.3
-3.53
0.11
0.032
0.043
7.2
0.84
2.1
1.11
1
113
156.5
D4
-1.1
-0.4
-28.1
27.0
-1.51
0.59
0.011
5.6
0.023
0.13
5.5
7.1
1.2
1.4
0.42
1.6
114
158
D4
8.1
7.4
1.1
1.6
0.54
3.5
-23.3
0.065
D4
0.008
160
4.3
116
117
166
D4
-26.1
0.4
0.008
0.044
5.5
1.9
1.2
2.1
0.19
0.6
118
167
D4
0.4
-27.8
28.2
-3.41
0.1
0.18
2.7
0.23
0.2
D4
-1.4
-26.5
25.1
0.7
168.5
0.99
119
-2.5
0.96
1.1
0.92
0.34
0.6
120
168.6
D4
-1.3
-1.9
-28.5
27.2
1.2
0.99
0.96
0.43
0.8
121
172.2
D4
3.3
-1.8
124
174
D4
4.7
-3.0
-27.1
31.8
125
175.5
D4
4.9
-1.7
-28
32.9
126
177.3
D4
129
179.8
D4
5.2
-4.5
-27
32.2
130
180
D4
5.4
-5.3
-25.6
31.0
132
182
D4
136
194
D4
1.8
137
200
DG
3.5
-0.6
138
200.1
DG
0.9
-2.8
138
-28.5
-26.5
4.1
-0.79
0.12
0.074
-26.3
-27.9
29.7
0.022
0.032
0.035
0.01
0.18
18
9.1
0.69
1.3
0.87
2.7
5.1
0.022
0.089
4
14.5
0.64
1.3
1.4
4.3
3.3
0.008
0.026
3.3
11
0.67
1.3
1.7
2.6
1.7
0.005
0.14
29
13
0.75
1.4
2
1.9
13
0.7
1.5
2
3.5
0.2
0.008
0.99
1.1
1.6
0.29
3.3
2.1
0.83
1.6
0.54
1.2
0.086
0.092
12
Chapter4:CdisotopevariationsinEdiacarancarbonates
sample
Height[m]
Member
δ Ccarb δ Ocarb δ Corg
Δδ 139
200.5
DG
140
201.5
DG
4.3
-5.0
141
203
DG
0.9
-2.8
142
205
DG
2.5
-2.2
143
205.5
DG
2.8
-1.0
144
207.5
DG
145
209
DG
146
213
DG
3.3
-4.0
147
216
DG
3.1
-3.9
148
217
DG
3.2
-3.4
13
1
18
1
13
13
ε
2SE
Cd[µg/g]
δ N
N[wt.%]
TOC[wt.%]
C/N
ΣREE[µg/g]
Ce/Ce* YN/HoN
PrN/YbN
EFMn(Cal-S)
0.8
1
1.6
0.24
4.9
-2.55
0.14
0.13
0.81
1
1.6
0.25
6.2
0.43
0.76
1.7
0.15
1.9
0.69
1
1.6
0.21
2.8
1.4
1.1
1.5
0.31
3.3
1.3
1.1
1.4
0.32
3.2
0.56
0.86
1.6
0.2
5.7
-2.19
0.10
0.074
0.51
0.88
1.6
0.18
2.7
0.62
0.73
1.8
0.21
2.9
0.69
0.83
1.8
0.23
2.5
112/110
2
Cd 15
3
4
139
Chapter5:Conclusions
CHAPTER5
CONCLUSIONS
This chapter is summarising the findings presented in the previous three chapters which are
designedforindividualpublication.Theeightmainfindingsare:
1.
The studied Ediacaran carbonates are affected by post-diagenetic alteration presumably
causedbyfluid-flowoverprint.Fluidsthatoverprintedthedeepwaterandslopefaciesshowa
different composition than those overprinting the shallow water sections on the Yangtze
Platform. In detail diagenetic fluid-flow led to a substantial redistribution of fluid-mobile
elements, notably, losses of Sr and Ba, and addition of radiogenic Sr and light oxygen from
typicalcontinentalbasinfluids.Inspiteofthealterationoffluid-mobileelements,amajorityof
carbonate rocks from the Yangtze Platform display primary shale normalised REE+Y patterns
thatpreservedthecompositionofthecoevalseawater.
2.
Comparedtoshallowwatersamples,carbonatesfromthedeepbasinontheYangtzePlatform
precipitatedinwaters,whichwerelikelymoreenrichedin 12C.Thedecouplingofδ13Ccarbfrom
δ13Corg within those carbonates may be explained by the partial remineralisation of organic
matterinthedeepmarineenvironment.
3.
Secularchangesintheseawaterchemistrybyevaporationanddilutionwithfreshwatermight
influencethetraditionalcarbonisotopesproxyusedforinter-profilecorrelation.Inparticular,
heavy δ13Ccarb values up to +9 ‰ at the top of the shallow water Xiaofenghe section may
indicatetemporarilyhighevaporationratesandhighsalinities.Giventhefactthatdilutionby
riverine inflow and evaporation under lagoonal conditions may have influenced Xiaofenghe
section, negative excursions of δ13Ccarb in the middle Doushantuo cannot be linked to other
profiles,neitherontheYangtzePlatform,norwithgloballyoccurringeventsliketheShuramWonokaexcursion.
4.
Shallow water carbonates at Xiaofenghe reveal 87Sr/86Sr values close to estimated global
Ediacaranseawater.ThecarbonatesalsopreservedtheirprimaryREE+Ypatterns,andelement
140
Chapter5:Conclusions
variations in the upper Doushantuo most likely reflect primary characteristics inherited from
localmixingoffreshwaterandseawaterinestuary-likeconditions.Indetailthemixingcaused
lesspronouncedY/HoanomaliesandrelativelyflatshalenormalisedREE+Ypatterns.
5.
The 87Sr/86Sr compositions rise at the end of the Ediacaran presumably as a result of an
increase of the 87Sr flux into the ocean by increased continental weathering. Because of
regionally enhanced weathering, Dengying samples at Xiaofenghe may be slightly more
radiogenic (0.7090) compared to 87Sr/86Sr in basal samples from the Dengying Formation at
othersectionsintheThreeGorgesarea.
6.
TheεNdivaluesofshallowwatercarbonatesatXiaofengheshowanarrowrangeoverlapping
with literature data from phosphorite and black shale samples from nearby locations. This
arguesforahomogenoushinterlandNdisotopiccompositionoferodingmaterialthroughmost
oftheEdiacaran.
7.
In the deep water carbonate samples redox-sensitive elements like Fe, Mo, U and V are
depleted compared to Phanerozoic carbonates, whereas Mn and Ba are strongly enriched,
suggestinganoxicandevensulfidicpore-waterconditionsinthedeepEdiacaranocean.
8.
Ediacaran carbonate leachates at Xiaofenghe show Cadmium isotope fractionation with
temporal evolution to light isotopic compositions. The variation of ε112/110Cd signals overlaps
withvaluesreportedformodernshallowseawater.However,thereasonsforthefractionation
ofCdisotopesismostlikelyaresultofinorganicprocesses,suchasprecipitationofauthigenic
sulphides under anoxic pore-water conditions in the lower Doushantuo and changes in the
fractionation rate due to variable salinity in the upper Doushantuo as a result of seawaterfreshwatermixinginanestuarine-likeenvironment.
141
Chapter6:Scientificoutput
CHAPTER6
SCIENTIFICOUTPUT
6.1PEERREVIEWEDPUBLICATIONS
Hohl, S.V, Becker, H., Herzlieb, S. and Guo, Q. (2015): Multiproxy constraints on alteration and
primary compositions of Ediacaran deep water carbonate rocks, Yangtze Platform, South China
publishedinGCA,2015
Gamper, A., Struck, A., Ohnemueller, F., Heubeck, C. and Hohl, S.V. (2015): Chemo- and
biostratigraphy of the Gaojiashan section (Northern Yangtze Platform, South China): A new Pc-C
boundarysection.
publishedinFossilRecord,2015
6.2SUBMITTEDMANUSCRIPTS
Hohl, S.V., Becker, H., Gamper, A., Jiang, S. Y., Wiechert, U., Yang, J.-Y. and Wei, H.Z.: Secular
changes of water chemistry in shallow water Ediacaran ocean: Evidence from carbonates at
Xiaofenghe,ThreeGorgesarea,YangtzePlatform,SouthChina.
SubmittedtoPrecambrianResearch,April2015(currentlyunderreview)
Sun, S., Heubeck, C., Hippler, D. and Hohl, S.V.: The nature of the Ediacaran-Cambrian contact at
Meishuncun,YunnanProvince,China.
SubmittedtoJournaloftheGeologicalSocietyofLondon,May2015
6.3UNPUBLISHEDMANUSCRIPTS
Hohl, S.V., Galer, S.J., Gamper, A and Becker, H.: Cadmium isotope variations in Neoproterozoic
carbonates-Atracerforredoxprocessesandwatermassmixing?
Hohl, S.V., Becker, H. Jiang S.Y and Guo, Q.: Geochemistry of Ediacaran cap dolostones of the
YangtzePlatform,SouthChina.
Rodler, A., Hohl, S.V., Guo, Q. and Frei, R: Chromium isotope stratigraphy of Ediacaran cap
carbonates,DoushantuoFormation,SouthChina.
142
Chapter6:Scientificoutput
6.4CONFERENCEABSTRACTSANDPRESENTATIONS
Hohl,S.V.,Galer,S.J.andBecker,H.(2015):CdisotopicvariationsinEdiacarancarbonaterocksfrom
SouthChina;Biogenicorabiogenicisotopefractionation?
OralpresentationatGoldschmidtConference2015,Prague
Hohl,S.V.,Becker,H.,Gamper,A.,Jiang,S.-Y.,Wiechert,U.andWei,H.(2014a):Multi-proxystudy
ofshallowwaterEdiacarancarbonates(Xiaofenghe,YangtzePlatform,SouthChina).
PosterpresentationattheGSAMeeting2014,Vancouver
Hohl, S.V., Galer, S.J. and Becker, H. (2014b): Cadmium isotopic fractionation in Ediacaran
carbonatesfromtheshallowwaterXiaofenghesection,YangtzePlatform,SouthChina.
OralpresentationattheGSAMeeting2014,Vancouver
Hohl,S.V.,Becker,H.,Herzlieb,S.,Guo,QandGamper,A.(2013):Multi-proxystudyofshallow-and
deepwaterDoushantuocarbonates,YangtzePlatform,SouthChina.
PosterpresentationattheGoldschmidtConference2013,Florence
Hohl, S.V.,Becker,H.,Hippler,D.andBäro,W.(2012a):TraceelementabundancesinDoushantuo
capdolostonesfromplatformandslopesettings,YangtzePlatform,SouthChina.
PosterpresentationattheGoldschmidtConference2012,Montreal
Hohl, S.V.,Becker,H.,Hippler,D.andBäro,W.(2012b):TraceelementabundancesinDoushantuo
cap dolostones from platform and slope settings, Yangtze Platform, South China - Influence of
calcificationandpostsedimentaryfluid-flow.
PosterpresentationattheGeologicalSocietyofLondon,Fermormeeting,2012
6.5GRADUATETHESISSUPERVISION
Steffen Herzlieb (2013): Element- und Isotopenzusammensetzungen von Karbonatgesteinen der
BeckenfaziesdesEdiacariumsderYangtzePlattform(Südchina),M.Sc.thesis,FreieUniversitätBerlin.
143
AppendixI:Fieldwork
APPENDIX
AI:FIELDWORK
Inordertoobtainrepresentativerocksamplesfromshallow-anddeepwatermarinefacies
fromtheEdiacaranweconductedfieldworkontheYangtzePlatform,SouthChinainspring2012,
samplingseveralsectionsinHunanandHubeiProvince.Thevisitedsedimentprofileswerechosen
basedonvariousfactors,suchasexistingdetailedsedimentologicaldescriptionsandcarbonisotope
compositiondatasets.ThefieldworkwasperformedwiththehelpoftheChinesecounterpartwithin
the Sino-German joint Research Group FOR 736. Of particular interest were the shallow water
Doushantuo Formation and overlying Dengying Formation in the Three Georges Region, Hubei
ProvinceandthedeepwaterfaciesofDoushantuo,HunanProvince.
Forthisdissertationproject,theDoushantuoFormationatXiaofenghesectionwassampled
in high resolution from the base of the cap carbonates into the first meters of the overlying
DengyingFormation.Thenorthernpartofthesection,abbreviatedas“NXF”,startswithabout4.8m
of cap dolomites with a clearly outcropping boundary to the diamictites of the Nantuo Formation
below.Followinganintervalcoveredbyvegetation,MemberD2beginswithinterlayereddolostones
and shales with thin chert layers. At 23 m, a 6 m thick sequence of 10-20 cm thick phosphoritic
layers in black shales crop out. The rest of D2 is dominated by alternating organic-rich carbonates
andmudstoneswithpea-sizedchertnodules.At102m,stratigraphicheighta1mthickblackshale
layer occurs. The shale is overlain by a massive dolostone- and organic-rich limestone unit, which
can be followed in the field until 136 m above the diamictites. We assume that the boundary
between D2 and D3 should be within or a few meters above the black shale horizon at 102m.
Further sampling of the section was continued on the southern flank of the valley at Xiaofenghe
village.Thispartofthesectionisabbreviatedas“SXF”.Followingthedescriptionof(M.Zhuetal.,
2013),usingtheprominentblackshalelayeratthetopofD2atNXFandSXFasamarkerhorizon,it
is possible to follow the stratigraphy of the SXF profile up to 225 m above the diamictites, which
includestheboundarybetweentheDoushantuoandtheoverlyingDengyingFormation.MemberD4
consists of silty/sandy dolostones with decimetre-sized chert nodules interbedded with pure
limestones (up to 99% calcite present). The upper Doushantuo Formation in the very shallow
regimes like at Xiaofenghe section seems to be more influenced by clays, or in the case of the
Hushan Dayukou section (Hubei, Province), sandy and silty dolostones (M. Zhu et al., 2013).
ThereforeitseemsquestionableiftheupperDoushantuodepositednorthoftheHuanglinganticline
144
AppendixI:Fieldwork
canbecorrelatedwiththeD4ofthedepositionalenvironmentintheYangtzeGeorgesareawhereit
consistsofblackshalesandkarstsurfacesmarkthetransitiontotheoverlyingDengyingFormation
(M.Zhuetal.,2007;Linetal.,2011).
SamplesfromYanwutansectionusedforgeochemicalanalysisinthefirstManuscriptwere
takenonanearlierfieldcampaignofFOR736Sino-GermanResearchGroupandresultshavebeen
publishedinGuoetal.(2007).
We furthermore sampled cap carbonates at various sections in Hubei and HunanProvince
throughout the Yangtze Platform from shallow water platform to deep water basin sedimentation
environments.WealsoincorporatedsamplesfrompreviousfieldcampaignstoHunanandGuizhou
Province into our composite study. The results of the analysed cap carbonates are subject of a
manuscriptthatwillbesubmittedinfall2015butisnotincorporatedintothisdissertation.
TableA1.fieldworkandanalysedsections
S ECTION F ORMATIONS
C OORDINATES
P ROXIES
P UBLICATIONS
X IAOFENGHE
H UBEI
C APCARBS
DS,DY
N30°56’29.5’’
E111°13’57.4’’
REE,
S R,N D ,N,C D ,
C,O
H OHLETAL
.,
P REC.R ES.2015
(INREVIEW )
JIJIAWAN
H UBEI
C APC ARBS
N30°52’59.9’’
E110°52’45.4’’
REE,
S R,C,O
H UAJIPO H UBEI
C APC ARBS
N30°46’54.4’’
E111°02’02.1’’
REE,
S R,C,O
H UANGLIANBA
Guizhou
C APC ARBS
N28°11’34.3’’
E°10915’39.5’’
REE,
S R,C,O
L ONGBIZUI
Hunan
C APC ARBS
N28°29’57.9’’
E109°50’28.0’’
REE,
S R,C,O
Y ANWUTAN
Hunan
C APC ARBS
DS
N28°25´20.0´´
E110°28´42.1´´
REE,
S R,C,O
capcarbonate
datayetto
publish
G UOETAL.,
2007;H OHLET
AL ., GCA 2015
DS=Doushantuo,DY=Dengying
145
AppendixI:Fieldwork
FIG .AI
Localities of sampled sections
on the Yangtze Platform.
Paleodepthinferredfromthe
paleo-geographical map after
Jiang et al. (2007). Shallow
watersections:1=Jijiawan;2
= Xiaofenghe; 3 = Huajipo (all
HubeiProvince);slopesection:
4 = Huanglianba (Guizhou
Province); basin sections: 5 =
Longbizui;6=Yanwutan(both
HunanProvince).
AII:ANALYTICALPROTOCOL
Priortocarbonateleachingchemistrywepreparedpolishedthicksectionsofcarbonaterock
chips embedded in araldite resin and coated them with a thin gold layer. Following up we prescreened the samples for possible alteration features, such as dedolomitisation or calcitic veins,
usingaZeissSupra40VPUltraSEMcoupledwithanOxfordInstrumentsEDXanalyser.Asaresultwe
were able to obtain sample powder by micro drilling into presumably unaltered areas. We further
prepared thin sections of selected cap carbonate samples. Staining the thin sections using alizarin
redcalcitestainingandFe-dolomitestainingmethodshelpedinunderstandingtheirgenesis.
For trace- and major element concentration analysis 20 to 50mg of finely grounded
carbonate powder were commonly reacted with 1 ml 1 M acetic acid at 70°C over night and the
solutioncentrifugedandfilteredthrough0.45µmcelluloseacetatefilters.Theelutewasdrieddown,
redissolvedanddilutedin0.28MHNO3forfinalmeasurement.Allmeasurementswereperformed
on a Thermo Finnigan Element XR sector-field ICP mass spectrometer at Freie Universität Berlin
usingaScotttypequartzspraychamberanda100µl/minnebulizer.Sampletimewas120swith20
samples/peakand60totalscans.Withthisanalyticalsetuptuninggenerallyyieldedlowoxiderates
of 2-5 % CeO+ and less than 1 % BaO+. We determined element concentrations by external
calibration to the matrix-matching CAL-S carbonate standard (Yeghicheyan et al., 2003). For drift
146
AppendixII:Analyticalprotocol
correction the diluted samples were doped with solutions of 2 ppb In and 1 ppb Tl for elements
analysed in low resolution mode (REE, Y, Rb, Pb, Sr, Mo, Cd, In, Tl, P, Th, U), and 12.5 ppb Co for
elementsanalysedinmediumresolutionmode(Mg,Al,Ca,Mn,Cr,Fe,Co,K,V,Zn,Ti).Background
corrections were performed by subtraction of the raw intensities of aspirated 0.28 M HNO3. The
analyticalprecisionswereusuallybetterthan5%(1SD)formostREE,Y,Rb,Cd,Ti,Zn,Ba,Pb,Mg,Al,
Ca,Mn,K,Th,10%forSr,U,V,FeandLaandabove10%(1SD)forCrandMo.Proceduralblankson
mosttraceelementsandREEwereweregenerallybelowtheacidbackgroundsignalintensities.
AliquotsoftheaceticacidleachateswereusedforSrisotopiccompositionmeasurements.
Approximately1µgSrwasloadedin2.5MHClon1mlAG50W-X8(200-400mesh)cation-exchange
resinforseparationofSrfromthematrix.TheStrontiumisotopiccompositionwasdeterminedusing
aThermo-FinniganTritonTIMSatFUBerlin.RepeatedmeasurementsofSRM987yielded 87Sr/86Sr=
0.710246 (±10, n=97). Mass fractionation was corrected assuming a 86Sr/88Sr ratio = 0.1194 (Nier,
1938)andtheexponentiallaw.Minorinterferencesof 87Rbon 87Srwerecorrectedusing 85Rb/87Rb=
2.59265. Initial 87Sr/86Sr were calculated assuming depositional ages according to the stratigraphic
position of the samples, 87Rb/86Sr ratios (calculated from ICP-MS data) and a half-life of 87Rb of
4.88×1010years.Correctionsofradiogenicingrowthwereusuallybelow0.5‰.
50mgofsamplepowderwereaddedtoanadequateamountof 148Ndand 147Smspikeand
then reacted with 2ml 0.5 M acetic acid over 12h, centrifuged and filtered through 0.45 µm PTFE
syringe filters. After drying down the supernatant was redissolved in 2.5 M HCl and REE bulk
separation was achieved by column separation using AG 50W-X8 (200-400 mesh) cation exchange
resin. The REE were then further separated by dissolving the supernatant in 200 µl 0.15 M HCl
followed by loading on ion exchange columns filled with Ln-Spec resin. Sm and Nd isotopic
measurements were performed on a Thermo Finnigan Neptune Plus multicollector ICP-MS at the
StateKeyLaboratoryforMineralDepositsResearchatNanjingUniversity,PeoplesRepublicofChina.
AcombinedScottandCyclonequartzspraychamberandaPFAnebulizerwith100µl/minwereused
with 5 runs and 10 passes for each sample, 300 s baseline and standard/sample bracketing
performedtocorrectforinstrumentaldrift.
Thefollowingcupconfigurationwasapplied:
L4
Pr
141
L3
Nd
142
L2
Nd
143
L1
Nd
144
C
Nd
145
H1
Nd
146
H2
Sm
147
H3
Nd
148
H4
Nd
150
147
AppendixII:Analyticalprotocol
Raw Nd isotope ratios were normalised to a 146Nd/144Nd of 0.7219 (O'Nions et al., 1977).
Repeated measurements (n=5) of a 50 ppb Ames Nd solution yielded 143Nd/144Nd = 0.511955 ±
0.000013 (2SD) and a 25 ppb Ames Nd solution yielded 143Nd/144Nd = 0.511944 ± 0.000021 (2SD)
(n=4). The initial ratio of 143Nd/144Nd at a given time is expressed as deviation from CHUR at that
timeintheformofεvalues,calculatedwithvaluesfor 147Sm/144NdCHURof0.196and 143Nd/144NdCHUR
of0.51263(Bouvieretal.,2008)andagesinferredfromstratigraphy.
Stable isotopes of C and O in carbonate were determined in-house. The isotope ratio
measurementswerecalibratedtoVienna-PeeDeeBelemnite(V-PDB)withCarraramarble(CAM)and
acalcite-carbonatite(KKS)asin-housestandards.Wereportisotoperatiosaspermilldeviationfrom
theinternationalreferencematerialV-PDBinthedeltanotationaccordingtoCoplen(2011).These
in-house reference materials were previously calibrated using NBS-19 (δ18O = -2.20 ‰ and δ13C =
+1.95‰)andNBS-18(δ18O=-23‰andδ13C=-5.01‰).Theexternalerrorsofthemeasurements
are±0.06‰(1SD)forδ18Oand±0.03‰(1SD)forδ13C,basedonthereproducibilityofanin-house
limestonereferencematerial(LM)andtheNBS-19standard.
Stableisotoperatiosandconcentrationmeasurementsofnitrogenandorganiccarbonwere
obtained using a Thermo-Finnigan MAT V isotope ratio mass spectrometer coupled to a Thermo
Flash EA 1112 elemental analyser via a Thermo/Finnigan Conflo III-interface at the Museum für
Naturkunde Berlin. δ15N analyses were performed on the bulk rock powder whereas for
13
Corg
measurementssamplepowdersweredecalcifiedusing2MHCl.Isotopicratiosareexpressedinthe
conventional delta notation relative to AIR and the V-PDB (Vienna PeeDee Belemnite) standard,
respectively.Thestandarddeviationforrepeatedmeasurementsofalaboratorystandardmaterial
(peptone)isgenerallybetterthan0.2‰.AftersamplecombustionaCO2-trapwasusedtoreduce
interferences between bulk rock nitrogen and carbon isotope signals. δ15N and δ13Corg values of
sampleswithanalysednitrogenandorganiccarboncontents<0.01mgand<0.04mg,respectively,
areomittedfromourinterpretationduetolowsignalintensitiesandpoorprecisionandaccuracy.
Cd isotopic compositions were determined with the help of the Max Planck Institute for
Chemistry,Mainz.Fortheseparationwereacted1mgofsamplepowderwith50mlof1Macetic
acid buffered to a pH of 5. Samples were spiked with a 106Cd – 108Cd double spike following the
procedures described in Schmitt et al. (2009). The Cd separation and purification was achieved by
usingtworunsoverPolyprepcolumnsfilledwith200µlofBioRadAG1-X8,100-200meshinnitric
form and elution with 0.25 N HNO3. The samples were loaded onto single Re filaments analysed
using a Thermal Ionisation Mass Spectrometer (TIMS) of type Thermo Finnigan Triton at the Max
PlanckinstituteforChemistryinMainz.Therawdatawascorrectedofflineforinternalinstrument
148
AppendixII:Analyticalprotocol
massfractionationusingtheexponentiallaw.Theachieveddataisexpressedinepsilon (ε)notation
relative to the reference standard material NIST SRM 3108. The Cd concentrations have been
obtainedbyisotopicdilution,showinggeneralanalyticaluncertaintiesoflessthen0.1%.
REFERENCES
Bouvier,A.,Vervoort,J.D.,Patchett,P.J.,2008.TheLu–HfandSm–NdisotopiccompositionofCHUR:
constraints from unequilibrated chondrites and implications for the bulk composition of
terrestrialplanets.EarthandPlanetaryScienceLetters.doi:10.1016/j.epsl.2008.06.010
Coplen, T.B., 2011. Guidelines and recommended terms for expression of stable isotope ratio
and gas
ratio measurement results. Rapid Communications in Mass Spectrometry.
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Guo,Qingjun,HaraldStrauss,CongqiangLiu,TatianaGoldberg,MaoyanZhu,DaohuiPi,
Christoph Heubeck, Elodie Vernhet, Xinglian Yang, and Pingqing Fu, 2007. Carbon Isotopic
Evolution of the Terminal Neoproterozoic and Early Cambrian: Evidence From the Yangtze
Platform, South China.” Palaeogeography, Palaeoclimatology, Palaeoecology 254, 140–57.
doi:10.1016/j.palaeo.2007.03.014.
Hohl,S.V.,Becker,H.,Herzlieb,S.,Guo,Q.,2015.Multiproxyconstraintsonalterationandprimary
compositions of Ediacaran deep water carbonate rocks, Yangtze Platform, South China.
GeochimicaetCosmochimicaActa163,262–278.doi:10.1016/j.gca.2015.04.037
Jiang,G.,Kaufman,A.J.,Christie-Blick,N.,Zhang,S.,Wu,H.,2007.Carbonisotopevariabilityacross
the Ediacaran Yangtze Platform in South China: Implications for a large surface-to-deep ocean
δ13C
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Lin, Z., Wang, Q., Feng, D., Liu, Q., Chen, D., 2011. Post-depositional origin of highly 13C-depleted
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stablecarbonisotopes.SedimentaryGeology242,71–79.doi:10.1016/j.sedgeo.2011.10.009
Nier,A.,1938.TheIsotopicConstitutionofStrontium,Barium,Bismuth,ThalliumandMercury.Phys.
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in oceanic basalts. Earth and Planetary Science Letters 34, 13–22. doi:10.1016/0012821X(77)90100-5
Schmitt, A.-D., Galer, S.J.G., Abouchami, W., 2009. High-precision cadmium stable isotope
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1079.doi:10.1039/b821576f
Yeghicheyan,D.,Carignan,J.,Valladon,M.,BouhnikLeCoz,M.,Samuel,J.,BenBakkar,M.,Bruguier,
O., Keller, F., Pin, C., Pourtales, L., 2003. The new carbonate reference material Cal–S:
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Zhu,M.,Zhang,J.,Yang,A.,2007.IntegratedEdiacaran(Sinian)chronostratigraphyofSouthChina.
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Zhu, M., Lu, M., Zhang, J., Zhao, F., Li, G., Aihua, Y., Zhao, X., Zhao, M., 2013. Carbon isotope
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149
AppendixIII:Curriculumvitae
AIII:CURRICULUMVITAE
Forreasonsofdataprotection,
thecurriculumvitaeisnotincludedintheonlineversion
150
AppendixIII:Curriculumvitae
Forreasonsofdataprotection,
thecurriculumvitaeisnotincludedinthisversion
151

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